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Posted by hackermondev 12/18/2025

We pwned X, Vercel, Cursor, and Discord through a supply-chain attack(gist.github.com)
1167 points | 433 comments
superasn 12/18/2025|
This is a pretty scary exploit, considering how easily it could be abused.

Imagine just one link in a tweet, support ticket, or email: https://discord.com/_mintlify/static/evil/exploit.svg. If you click it, JavaScript runs on the discord.com origin.

Here's what could happen:

- Your Discord session cookies and token could be stolen, leading to a complete account takeover.

- read/write your developer applications & webhooks, allowing them to add or modify bots, reset secrets, and push malicious updates to millions.

- access any Discord API endpoint as you, meaning they could join or delete servers, DM friends, or even buy Nitro with your saved payment info.

- maybe even harvest OAuth tokens from sites that use "Login with Disord."

Given the potential damage, the $4,000 bounty feels like a slap in the face.

edit: just noticed how HN just turned this into a clickable link - this makes it even scarier!

jdsleppy 12/18/2025||
Doesn't stealing the cookies/token require a non-HTTP-only session cookie or a token in localstorage? Do you know that Discord puts their secrets in one of those insecure places, or was it just a guess?

I believe if you always keep session cookies in secure, HTTP-only cookies, then you are more resilient to this attack.

I interviewed frontend devs last year and was shocked how few knew about this stuff.

notnullorvoid 12/18/2025|||
In general if a script can run, users sessions and more importantly passwords are at risk.

It's true that an HTTP-only session cookie couldn't be directly taken, but it's trivial to present the user with a login screen and collect their password (and OTP), at which point you can easily get a session remotely. It can look entirely like the regular login page right down to the url path (because the script can modify that without causing a page load).

socketcluster 12/19/2025|||
Yep, httpOnly cookies just give the hacker a bit of extra work in some situations. TBH I don't even think httpOnly is worth the hassle it creates for platform developers given how little security it adds.
drewvlaz 12/19/2025||||
Wow did not realize a url could be set like that without promoting a page reload...
notnullorvoid 12/19/2025|||
To be clear only the path and query parameters part of the url can change, the domain (or sub domain) stays intact.
sdf456 12/19/2025|||
Even scarier to me than the vulnerability is that Fidelity (whom I personally think is a good bank and investment company) was using a third party that allowed injection that could potentially steal a whole lot of money, affect markets, ruin or terminate billions of lives, and affect the course of humanity. What the fuck.
DANmode 12/19/2025|||
Their knowledge of finance is certainly better than their knowledge of web tech.

Historically and today.

sebmellen 12/19/2025||||
That’s why I’m a Schwab junkie… but finance is a hotspot for this kind of stuff.
udev4096 12/19/2025|||
[dead]
9rx 12/19/2025|||
If it weren't already in the same domain you wouldn't be able to read a non-HttpOnly cookie anyway, so that's moot.
psnehanshu 12/19/2025|||
Well that's how SPAs work (single page applications)
jonfw 12/19/2025|||
How do you modify the url exactly?
eloisius 12/19/2025|||
https://developer.mozilla.org/en-US/docs/Web/API/History/pus...
notnullorvoid 12/19/2025|||
`history.replaceState(null, "", "/login")`
rvnx 12/19/2025||
For Coinbase docs, this is a disaster particularly
notnullorvoid 12/19/2025||
By they looks of it their docs are under a subdomain, and no part of the domain can be changed when setting the url this way. So it would still look a little out of place at least.
brianxq3 12/19/2025||
I mean, you're not wrong, but this is going to trick a non-zero number of people and that's not okay. We should expect more out of companies like Coinbase and hold them to a high standard.

This is unacceptable and the amount offered in general is low. It feels like we can agree on this.

Maxion 12/19/2025||
auth URLs are almost always a shitshow in every larger corp. Having the url be https://docs.bigcorp.com/sso/authlayerv1/us-east-24/aws/secu... would not stand out at all to anyone.
giancarlostoro 12/19/2025||||
No because Discord auth tokens dont expire soon enough. The only thing that kills them is changing your password. Idk why Discord doesnt invalidate them after some time, it is seriously amateur hour over there and has been for a while.
seaal 12/19/2025||
Probably because the end user hates login in, my friends always complain about the “remember me” button being useless for some services.
giancarlostoro 12/20/2025||
No, these are tokens that you get a new one per request, if you open up dev tools, and open the user settings panel, you will see that you get a new one every single time you open the user settings panel. They never expire, at least for years they were insanely long lasting.
ddlsmurf 12/18/2025||||
if you set the cookier header right (definitely not always the case), this is true, but the javascript can still send requests that will have that cookie included, effectively still letting the hacker use the session as the logged in user
collinmanderson 12/19/2025||
with http-only they can't _steal_ the cookie, but they can still _use_ the cookie. It reduces the impact but doesn't fully solve it.
hackermondev 12/18/2025||||
Discord puts the authentication token in local storage
edoceo 12/19/2025||
Is that a problem on its own? It's like, encrypted right? Maybe a time sensitive token?
socketcluster 12/19/2025|||
Not a problem in itself. Also, there's not much point of encrypting tokens. The attacker could use the encrypted token to authenticate themselves without having to decrypt. They could just make a request from the victim's own browser. They could do this with cookies too even with httpOnly cookies.

XSS is a big problem. If a hacker can inject a script into your front end and make it execute, it's game over. Once they get to that point, there's an infinite number of things they can do. They basically own the user's account.

arethuza 12/19/2025||
Does anyone actually encrypt the contents of JWTs? I'd have thought that anyone who has concerns about the contents of the token being easily visible would be likely to avoid JWTs anyway and just use completely opaque tokens?
kbolino 12/19/2025|||
Encrypted tokens are opaque but they are also offline-verifiable. A simple opaque token has to be verified online (typically, against a database) whenever it's used.

Auth0, for example, supports JWE for its access tokens: https://auth0.com/docs/secure/tokens/access-tokens/json-web-...

socketcluster 12/20/2025|||
JWT supports some encryption algorithms as an alternative to signatures but my experience is that most people like to keep it simple.

JWT is intended for authentication. Most of the time you're basically just signing a token containing an account ID and nothing else... Sometimes a list of groups but that only scales to a small number of groups.

seangrogg 12/19/2025|||
Depends on the token; JWTs usually have payloads that are only base64 encoded. As well, if there's a refresh token in there it can be used to generate more tokens until invalidated (assuming invalidation is built in).
s_ting765 12/18/2025||||
You may be thinking of CSRF mitigations. XSS exploits are more dangerous and can do more than steal sessions.
z3t4 12/19/2025||||
https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/...
abustamam 12/19/2025||||
As a FE dev, I wouldn't be able to articulate what you just did in the way you did, but it is something I know in practice, just from experience. I don't think any of the FE courses I took tackled anything like that.
j-krieger 12/19/2025||||
Token stealing hasn't been a real danger for a decade now. If you don't mark your token's as non-HTTP you're doing something explicitely wrong, because 99% of backends nowadays do this for you.
collinmanderson 12/19/2025||
with http-only they can't _steal_ the cookie, but they can still _use_ the cookie. It reduces the impact but doesn't fully solve it.
netdevphoenix 12/19/2025|||
Surely, if a script is in a position to sniff the cookie from local storage, they can also indirectly use the http-only cookie by making a request from the browser. So really not much of a difference as they will be taking over the account
Aldipower 12/19/2025||
The cookie storage and the local storage by all means is not the same! Cookies are not stored in the local storage and could be httpOnly, so they are not directly accessible by JavaScript. Nevertheless, as described above, with this XSS attack it is easy to bypass the token and just steal the user credentials by pretending a fresh login mask keeping the origin domain intact. That's why XSS attacks are dangerous since existence. Nothing new actually.
why-o-why 12/19/2025|||
The fact that it is just so trivial and obvious that its scary. It didn't even require any real hacking chops, just patience: literally anyone with a cursory knowledge of site design could have stumbled on this if they were looking at it.

Terrifying.

snvzz 12/18/2025|||
>the $4,000 bounty feels like a slap in the face.

And serves a reminder crime does pay.

In the black market, it would have been worth a bit more.

imdsm 12/19/2025|||
I was once only given $1,000 for an exploit where I could put in npm usernames and get their email addresses. Big corps don't always pay what they should.
doctorpangloss 12/19/2025||||
yeah, but nothing pays as much as doing free work for (checks notes) mintlify feels
tptacek 12/18/2025|||
No it would not have been.
notnullorvoid 12/19/2025|||
This specific XSS vulnerability may not have been, but the linked RCE vulnerability found by their friend https://kibty.town/blog/mintlify/ certainly would've been worth more than the $5,000 they were awarded.

A vulnerability like that (or even a slightly worse XSS that allowed serving js instead of only svg) could've let them register service workers to all visiting users giving future XSS ability at any time, even after the original RCE and XSS were patched.

tptacek 12/19/2025||
Maybe? I don't know enough about the vulnerability. Is it serverside? Then it isn't worth very much.
jrflowers 12/19/2025||
>i quickly realised that this was the server-side serverless (lol) environment of their main documentation app, while this calls to a external api to do everything, we have the token it calls it with in the env.

>alongside, we can poison the nextjs cache for everyone for any site, allowing mass xss, defacing, etc on any docs site.

tptacek 12/19/2025||
So it's a serverside bug that basically creates a more-severe stored DOM corruption vulnerability? Yeah, that's not worth anything to any buyer of vulnerabilities that I know exists. Maybe you know ones that I don't know.
jrflowers 12/19/2025||
I can’t speak to the value of the vulnerability as I lack the universal Rolodex of Every Exploit Buyer that is apparently available (nor am I interested in debating this with somebody that admitted they didn’t know anything about the vulnerability, declared it worthless anyway, and then moved the goalposts after a core assumption about it was trivially shown to be wrong. I’m fairly certain at this point these kids could recreate the end of the movie Antitrust and there’d be a thread somewhere with tptacek posting “This isn’t that big of a deal because”).

I just saw that you asked if the article about the server-side exploit was about a server-side exploit. It is. It’s right there in the post.

tptacek 12/19/2025||
Can I ask which exploit buyers you are aware of? None of us know all of them! It'll be easier to discuss this with a specific buyer in mind.
tuhgdetzhh 12/18/2025||||
Could you elaborate on why not?
tptacek 12/19/2025|||
What 'arcwhite said (sorry, I got dragged into a call).

1. The exploits (not vulnerabilities; that's mostly not a thing) that command grey/black market value all have half-lives.

2. Those exploits all fit into existing business processes; if you're imagining a new business, one that isn't actively running right now as we speak (such as you'd have to do to fit any XSS in a specific service), you're not selling an exploit; you're planning a heist.

3. The high-dollar grey market services traffic exclusively in RCE (specifically: reliable RCE exploits, overwhelmingly in mainstream clientside platforms, with sharp dropoffs in valuation as you go from e.g. Chrome to the next most popular browser).

4. Most of the money made in high-ticket exploit sales apparently (according to people who actually do this work) comes on the backend, from tranched maintenance fees.

arcwhite 12/18/2025|||
There's generally no grey market for XSS vulns. The people buying operationalized exploits generally want things that they can aim very specifically to achieve an outcome against a particular target, without that target knowing about it, and operationalized XSS vulns seldom have that nature.

Your other potential buyers are malware distributors and scammers, who usually want a vuln that has some staying power (e.g. years of exploitability). This one is pretty clearly time-limited once it becomes apparent.

Lionga 12/18/2025|||
It would have been. Ten times the amount at least.
mpeg 12/18/2025|||
For a reflected XSS? Tell me who is paying that much for such a relatively common bug...

To elaborate, to exploit this you have to convince your target to open a specially crafted link which would look very suspect. The most realistic way to exploit would be to send a shortened link and hope they click on it, that they are logged into discord.com when they do (most people use the app), that there are no other security measures (httponly cookies) etc

No real way to use this to compromise a large amount of users without more complex means

PenguinCoder 12/18/2025|||
It isn't about the commonality of the bug, but the level of access it gets you on the type or massive scale of the target. This bug you your blog? Who cares. This bug on Discord or AWS? Much more attractive and lucrative.
mpeg 12/18/2025|||
Yes, but this is not a particularly high access level bug.

Depending on the target, it's possible that the most damage you could do with this bug is a phishing attack where the user is presented a fake sign-in form (on a sketchy url)

I think $4k is a fair amount, I've done hackerone bounties too and we got less than that years ago for a twitter reflected xss

rvnx 12/19/2025||
Why would that be the maximum damage ? This XSS is particularly dangerous because you are running your script on the same domain where the user is logged-in so you can pretty much do anything you want under his session.

In addition this is widespread. It's golden for any attacker.

0x3f 12/19/2025||
Because modern cookie directives and browser configs neuter a lot of the worst XSS outcomes/easiest exploit paths. I would expect all the big sites to be setting them, though I guess you never know.
rvnx 12/19/2025|||
I would not be that confident as you can see: on their first example, they show Discord and the XSS code is directly executed on Discord.com under the logged-in account (some people actually use web version of Discord to chat, or sign-in on the website for whatever reason).

If you have a high-value target, it is a great opportunity to use such exploits, even for single shots (it would likely not be detected anyway since it's a drop in the ocean of requests).

Spreading it on the whole internet is not a good strategy, but for 4000 USD, being able to target few users is a great value.

Besides XSS, phishing has its own opportunity.

Example: Coinbase is affected too though on the docs subdomain and there are 2-step, so you cannot do transactions directly but if you just replace the content with a "Sign-in to Coinbase / Follow this documentation procedure / Download update", this can get very very profitable.

Someone would pay 4000 USD to receive 500'000 USD back in stolen bitcoins).

Still, purely with executing things under the user sessions there are interesting things to do.

promiseofbeans 12/19/2025|||
> some people actually use web version of Discord to chat, or sign-in on the website for whatever reason

Beside this security blunder on Discord’s part, I can see only upsides to using a browser version rather than an Electron desktop app. Especially given how prone Discord are to data mining their users, it seems foolish to let them out of the web sandbox and into your system

tptacek 12/19/2025|||
Again, here you have not so much sold a vulnerability as you have planned a heist. I agree, preemptively: you can get a lot of money from a well-executed heist!
rvnx 12/19/2025||
Do you want to execute actions as logged-in user on high-value website XXX ?

If yes -> very useful

tptacek 12/19/2025||
Nobody is disputing that a wide variety of vulnerabilities are "useful", only that there's no market for most of them. I'd still urgently fix an XSS.
rvnx 12/19/2025||
There is a market outside Zerodium, it's Telegram. Finding a buyer takes time and trust, but it has definitively higher value than 4k USD because of its real-world impact, no matter if it is technically lower on the CVSS scores.
tptacek 12/19/2025||
Really? Tell me a story about someone selling an XSS vulnerability on Telegram.

("The CVSS chart"?)

Moments later

Why do people keep bringing up "Zerodium" as if it's a thing?

rvnx 12/19/2025||
I understand your perspective about the technical value of an exploit, but I disagree with the concept that technical value = market value.

There are unorganized buyers who may be interested if they see potential to weaponize it.

In reality, if you want to maximize revenue, yes, you need to organize your own heist (if that's what you meant)

tptacek 12/19/2025|||
Do you know this or do you just think it should be true?
JumpCrisscross 12/19/2025|||
> understand your perspective about the technical value of an exploit

Going out on the world’s sturdiest limb and saying u/tptacek knows the technical and trading sides of exploits. (Read his bio.)

GoblinSlayer 12/19/2025|||
AIU this feature is SSS, not XSS, so XSS protections don't apply.
0x3f 12/18/2025|||
How would you make money from this? Most likely via phishing. Not exactly a zero-click RCE.
tptacek 12/18/2025||
What happens in all these discussions is that we stealthily transition from "selling a vulnerability" to "planning a heist", and you can tell yourself any kind of story about planning a heist.
varenc 12/19/2025|||
Also the XSS exploit would have been dead in the water for any sites using CSP headers. Coinbase certainly uses CSP. With this in place an XSS vuln can't inject arbitrary JS.
krainboltgreene 12/18/2025|||
I don't like tptacek, but it's insane to not back up this comment with any amount of evidence or at least explanation. The guy knows his shit.
tptacek 12/18/2025||
Hey I was wrong about Apple downthread.
panzi 12/19/2025|||
> - Your Discord session cookies and token could be stolen, leading to a complete account takeover.

Discord uses HttpOnly cookies (except for the cookie consent banner).

compootr 12/19/2025||
tokens are stored in localStorage, which is accessible by JS
johnisgood 12/19/2025||
Well, it used to be much more accessible before, now you have to do some hack to retrieve it, and by hack, I mean some "window.webpackChunkdiscord_app.push" kinda hack, no longer your usual retrieval. Basically you have to get the token from webpack. The localStorage one does not seem to work anymore. That is what I used, but now it does not work (or rather, not always). The webpack one seems to be reliably good.

So your code goes like:

  // Try localStorage first
  const token = getLocalStorageItem('token')
  if (token) return token

  // Try webpack if localStorage fails
  const webpackToken = await getTokenFromWebpack()
  if (webpackToken) return webpackToken
and localStorage does fail often now. I knew the reason for that (something about them removing it at some point when you load the website?) so you need the webpack way, which is consistently reliable.

I believe if you search for the snippet above, you can find the code for the webpack way.

None4U 12/19/2025||
Discord removes the token from localStorage when the web app is open and it's in app memory, and places it back when you close the tab using the "onbeforeunload" event.
johnisgood 12/20/2025||
Yeah, that is what I have observed, too.

You can retrieve it the webpack way though.

llmslave2 12/18/2025||
This feels so emblematic of our current era. VC funded vibe coded AI documentation startup somehow gets big name customers who don't properly vet the security of the platform, ship a massive vulnerability that could pwn millions of users and the person who reports the vulnerability gets...$5k.

If I recall last week Mintlify wrote a blog post showcasing their impressive(ly complicated) caching architecture. Pretending like they were doing real engineering, when it turns out nobody there seems to know what they're doing, but they've managed to convince some big names to use them.

Man, it's like everything I hate about modern tech. Good job Eva for finding this one. Starting to think that every AI startup or company that is heavily using gen-ai for coding is probably extremely vulnerable to the simplest of attacks. Might be a way to make some extra spending money lol.

tptacek 12/18/2025||
I don't think anybody in SFBA-style software development, both pre- and post-LLM, is really resilient against these kinds of attacks. The problem isn't vibe coding so much as it is multiparty DLL-hell dependency stacks, which is something I attribute more to Javascript culture than to any recent advance in technology.
tinco 12/18/2025|||
I wonder what's worse, the SFBA-style software development, but also with SFBA-style 2 hour response window to serious bugs like Discord showed, or the old fashioned enterprise report your bug and within 2 months you'll receive an e-mail confirming your report if you're lucky and a letter from a lawyer if you're not.
mattmanser 12/19/2025||||
It's got nothing to do with DLLs or libraries or anything like that. This is a bug in their domain code. This is a simple, and bloody stupid, multi-tenant bug in a SaaS where they're not checking the tenant id before serving tenant content. Coupled with exploiting same domain cookies. Both of these have been problems that we have dealt with, and been vigilant against in SaaS apps. We had a lot of these type of attacks in the 00s when people first started deploying SaaSes and for a while we were all vigilant. The common vector for cookies back then was you'd have your main app "acmeforce.com" and you'd host customers under sub-domains like "arasaka.acmeforce.com" and cookie shenanigans would allow all sorts of attack vectors against the root site (I think github had one at one point, might be wrong!).

It's more that browser changes have allowed us to forget cookie problems, in a good way. And software developers seem to have a memory of a goldfish. The browsers have tried to build in all sort of protections against these attacks, but they only work against different domains, so we hit all the same problems as soon as some inexperienced developers starts making a multi-tenant app without proper testing.

Aachen 12/19/2025||||
That's "San Francisco Bay Area" for anyone else wondering
alxndr 12/21/2025||
Is this synonymous with AI-assisted coding now??
Aachen 12/22/2025||
The person above implies as much. Doesn't mean anyone else thinks it
llmslave2 12/18/2025||||
You're right that it's a specific programming culture that is especially vulnerable to it. And for the same reasons they were vulnerable to the same thing to a lesser degree before the rise of LLMs.

But like, this case isn't really a dependency or supply chain attack. It's just allowing remote code execution because, idk, the dev who implemented it didn't read the manual and see that MDX can execute arbitrary code or something. Or maybe they vibe coded it and saw it worked and didn't bother to check. Perhaps it's a supply-chain attack on Discord et al to use Mintlify, if thats what you meant then I apologize.

I think you're right that I have an extreme aversion to SFBA-style software development, and partly because of how gen-ai is used there.

michaelt 12/18/2025||
One might consider this a supply chain attack because the title of the post is “We pwned X, Vercel, Cursor, and Discord through a supply-chain attack”
OrangeMusic 12/19/2025||
Sometimes titles are inaccurate
ajross 12/18/2025||||
You're preaching to the choir about the fragility of the the "dig the dependency stack all the way down to hell" paradigm. But I don't think it applies in this particular case (neither does attributing it to vibe coding, IMHO).

The component which ultimately executed the payload in the SVG was the browser, and the backend dependency stack just served it verbatim as specified by the user. This is a 1990's style XSS fuckup, not anything subtle.

macNchz 12/18/2025|||
I do occasionally wonder how different things would be if JavaScript had come with a very robust standard library from early on.
auxiliarymoose 12/19/2025|||
The crazy thing is that today the JavaScript standard library is very robust, and yet the culture of pulling in a ton of dependencies persists. It's so much easier to develop code against a stable and secure platform, yet it seems the choice is often to pull in hundreds of bits of code maintained by many different parties (instead of doing a little more in-house).
fireant 12/19/2025|||
I also wonder about it recently. Also in regards to Rust which is hailed as the great savior but has the same, minimal, approach to standard library and needs loads of dependencies.
kibwen 12/19/2025||
No, I wish people would let this meme die.

Rust doesn't have a very broad stdlib, but it has an extremely deep stdlib. Rust's stdlib is huge for the things it provides. Classical JS's stdlib was neither deep nor broad.

Furthermore, tons of those "loads of dependencies" that people point to are crates provided by the Rust project itself. Crates like serde, regex, etc aren't third-party dependencies, they're first-party dependencies just like the stdlib.

tick_tock_tick 12/18/2025|||
The issue is everyone loves to have everything fronted by a single domain. Most of xss is because of this basic flaw. All of this could have been avoided if discord didn't run their API docs through discord.com
__float 12/18/2025|||
It's a bit surprising they did that, to be honest. I work at a similarly-sized, HN-popular tech company and our security team is very strict about less-trusted (third party!!) code running on another domain, or a subdomain at the very least, with strict CSP and similar.

But in the age of AI, it seems like chasing the popular thing takes precedence to good practices.

joshdavham 12/19/2025||||
Thanks for this comment tick_tock :)

After reading this, I did some research and learned a lot. I never really considered that, by including many things under the same domain, that you're increasing your blast radius w.r.t security vulernabilites. Thanks for that

staticassertion 12/19/2025||||
This is what it really comes down to. Browsers are built around origins as the major security boundary. When you use a separate origin, safety comes for free.
integralid 12/19/2025|||
And you open another can of worms which is phishing. If you run your marketing campaigns from yourcompany-deals-2025.com don't be surprised when people click yourcompany-login.com links
staticassertion 12/20/2025||
I'm not sure I understand.

edit: That is, your phishing approach would work regardless, in my opinion. If your main site is `mycompany.com` then don't be surprised to see phishers sending `my-company.com` etc.

Also, you can host our content on a separate domain while still having users visit the same domain.

mock-possum 12/19/2025|||
Trust doesn’t though - discord.com/docs looks legit, as does docs.discord.com - discord-docs.com immediately sets off red flags
brap 12/19/2025|||
Is there no way to tell the browser “hey this URL is using the same domain but please isolate it from the rest”?
staticassertion 12/23/2025||
You can use a sandboxed iframe without an origin.
staticassertion 12/20/2025|||
You can still have discord.com/docs with content hosted on discord-docs.com
zahlman 12/19/2025||||
But then you have to be able to trust that the other domain is actually operated by Discord and isn't some social engineering front.
Banditoz 12/18/2025||
I'm curious what caching architecture a docs site needs, it can't be more complicated than a standard fare CDN?
0x3f 12/18/2025|||
Here's the other post:

https://news.ycombinator.com/item?id=46276313

mosura 12/18/2025|||
Search indexing, etc.
dllu 12/18/2025||
The fact that SVG files can contain scripts was a bit of a mistake. On one hand, the animations and entire interactive demos and even games in a single SVG are cool. But on the other hand, it opens up a serious can of worms of security vulnerabilities. As a result, SVG files are often banned from various image upload tools, they do not unfurl previews, and so on. If you upload an SVG to discord, it just shows the raw code; and don't even think about sharing an SVG image via Facebook Messenger, Wechat, Google Hangouts, or whatever. In 2025, raster formats remain way more accessible and easily shared than SVGs.

This is very sad because SVGs often have way smaller file size, and obviously look much better at various scales. If only there was a widely used vector format that does not have any script support and can be easily shared.

poorman 12/18/2025||
All SVGs should be properly sanitized going into a backend and out of it and when rendered on a page.

Do you allow SVGs to be uploaded anywhere on your site? This is a PSA that you're probably at risk unless you can find the few hundred lines of code doing the sanitization.

Note to Ruby on Rails developers, your active storage uploaded SVGs are not sanitized by default.

nradov 12/18/2025|||
Is there SVG sanitization code which has been formally proven correct and itself free of security vulnerabilities?
codedokode 12/19/2025||||
It would be better if they were sanitized by design and could not contain scripts and CSS. For interactive pictures, one could simply use HTML with inline SVG and scripts.
poorman 12/18/2025||||
GitLab has some code in their repo if you want to see how to do it.
jdironman 12/19/2025||
This is what they actually use: https://github.com/flavorjones/loofah
rcxdude 12/18/2025||||
Sanitisation is a tricky process, it can be real easy for something to slip through the cracks.
auxiliarymoose 12/19/2025|||
Yes. Much better to handle all untrusted data safely rather than try to transform untrusted data into trusted data.

I found this page a helpful summary of ways to prevent SVG XSS: https://digi.ninja/blog/svg_xss.php

Notably, the sanitization option is risky because one sanitizer's definition of "safe" might not actually be "safe" for all clients and usages.

Plus as soon as you start sanitizing data entered by users, you risk accidentally sanitizing out legitimate customer data (Say you are making a DropBox-like fileshare and a customer's workflow relies on embedding scripts in an SVG file to e.g. make interactive self-contained graphics. Maybe not a great idea, but that is for the customer to decide, and a sanitization script would lose user data. Consider for example that GitHub does not sanitize JavaScript out of HTML files in git repositories.)

lelandfe 12/18/2025||||
Yeah I’ve worked on a few pieces of software now that tried SVG sanitizing on uploads, got hacked, and banned the uploads.
exceptione 12/18/2025|||
I guess it is a matter of parsing svg. Trying to hack around with regex is asking for trouble indeed.
ivw 12/18/2025|||
just run them through `svgo` and get the benefits of smaller filesizes as well
silverwind 12/19/2025||
svgo is a minifier, not a sanitizer.
ivw 12/20/2025||
I should have clarified `svgo + removeScripts`

https://svgo.dev/docs/plugins/removeScripts/

aidenn0 12/18/2025|||
External entities in XML[1] were a similar issue back when everyone was using XML for everything, and parsers processed external-entities by default.

1: https://owasp.org/www-community/vulnerabilities/XML_External...

Sohcahtoa82 12/18/2025|||
XXE should have never existed.

Whoever decided it should be enabled by default should be put into some sort of cybersecurity jail.

GoblinSlayer 12/19/2025||
It's no different from links to googlesyndication in offline html docs.
hinkley 12/18/2025|||
At least with external entities you could deny the parser an internet connection and force it to only load external documents from a cache you prepopulated and vetted. Turing completeness is a bullshit idea in document formats.
actionfromafar 12/18/2025|||
Postscript is pretty neat IMHO and it’s Turing complete. I really appreciated my raytraced page finally coming out of that poor HP laser after an hour or so.
aidenn0 12/18/2025|||
I once sent a Sierpinski's Triangle postscript program to a shared printer. It took 90 minutes, and pissed off everybody else trying to print.
anthk 12/18/2025||||
PostScript can emulate the ZMachine (Zork text adventures and all of infocom) with "zmachine.ps". Look it up at DDG/GG.
zahlman 12/19/2025||
How does it do I/O?
actionfromafar 12/19/2025||
A monad. It’s just a class of abstract Endor Moon or something. Probably you have to send all commands up to the current state to it. :)
hinkley 12/18/2025||||
One of the very first SVG documents I encountered was a port of the PS Tiger to SVG. It loaded a lot faster than the PostScript Tiger.
bigfatkitten 12/18/2025|||
Sounds almost like a fun crypto mining opportunity.
aidenn0 12/18/2025||||
With SVGs you can serve them from a different domain. IIUC the issue from TFA was that the SVGs were served from the primary domain; had they been on a different domain, they would have not been allowed to do as much.
gnerd00 12/18/2025|||
calling Leonard Rosenthol ...
socalgal2 12/19/2025|||
IIUC, an untrusted inline SVG is bad. An image tag pointing to an SVG is not.

    <img src="untrusted.svg"> <!-- this is ok -->
    <svg from untrusted src>  <!-- this is not ok -->
I feel like this is common knowledge. Just like you don't inject untrusted HTML into your page. Untrusted HTML also has scripts. You either sanitize it. OR you just don't allow it in the first place. SVG is, at this point, effectively more HTML tags.
auxiliarymoose 12/19/2025||
Also remember that if the untrusted SVG file is served from the same origin and is missing a `Content-Disposition: attachment` header (or a CSP that disables scripts), an attacker could upload a malicious SVG and send the SVG URL to an unsuspecting user with pretty bad consequences.

That SVG can then do things like history.replaceState() and include <foreignObject> with HTML to change the URL shown to the user away from the SVG source and show any web UI it would like.

socalgal2 12/19/2025||
how is that special/different from an HTML URL?
auxiliarymoose 12/20/2025||
Because displaying user-submitted images is pretty common and doesn't feel like a security footgun, but displaying user-submitted HTML is less common (and will raise more careful security scrutiny).
bobbylarrybobby 12/18/2025|||
Would it be possible for messenger apps to simply ignore <script> tags (and accept that this will break a small fraction of SVGs)? Or is that not a sufficient defense?
demurgos 12/18/2025|||
I looked into it for work at some point as we wanted to support SVG uploads. Stripping <script> is not enough to have an inert file. Scripts can also be attached as attributes. If you want to prevent external resources it gets more complex.

The only reliable solution would be an allowlist of safe elements and attributes, but it would quickly cause compat issues unless you spend time curating the rules. I did not find an existing lib doing it at the time, and it was too much effort to maintain it ourselves.

The solution I ended up implementing was having a sandboxed Chromium instance and communicating with it through the dev tools to load the SVG and rasterize it. This allowed uploading SVG files, but it was then served as rasterized PNGs to other users.

MarsIronPI 12/18/2025||
Shouldn't the ignoring of scripting be done at the user agent level? Maybe some kind of HTTP header to allow sites to disable scripts in SVG ala CORS?
demurgos 12/20/2025|||
It's definitely a possible solution if you control how the file are displayed. In my case I preferred the files to be safe regardless of the mechanism used to view them (less risk of misconfiguration).
antiloper 12/19/2025|||
Content-Security-Policy: default-src 'none'
staticassertion 12/19/2025|||
No, svgs can do `onload` and `onerror` and also reference other svgs that can themselves contain those things (base64'd or behind a URI).

But you can use an `img` tag (`<img src="evil.svg">`) and that'll basically Just Work, or use a CSP. I wouldn't rely on sanitizing, but I'd still sanitize.

collinmanderson 12/19/2025||
> But you can use an `img` tag (`<img src="evil.svg">`) and that'll basically Just Work

That doesn't help too much if evil.svg is hosted on the same domain (with default "Content-Type: image/svg+xml" header), because attacker can send a direct link to the file.

GoblinSlayer 12/19/2025||
Reddit horribly breaks direct links to images and serves html instead.
Wowfunhappy 12/18/2025|||
IMO, the bigger problem with SVGs as an image format is that different software often renders them (very) differently! It's a class of problem that raster image formats basically don't have.
josefx 12/19/2025|||
> It's a class of problem that raster image formats basically don't have.

That took way too long to be this way. Some old browsers couldn't even get the colors of PNGs correct, let alone the transparency.

zffr 12/18/2025||||
I would have expected SVGs to be like PDFs and render the same across devices. Is the issue that some renderers don’t implement the full spec, or that some implement parts incorrectly?
lenzm 12/18/2025|||
They are like PDFs in that they do not render the same with different software or on different devices.
Wowfunhappy 12/19/2025|||
I would say PDFs are actually reasonably consistent though. Weird things happen on occasion, but I've certainly had more success than with SVGs.
auxiliarymoose 12/19/2025||
They are reasonably consistent because there is a de-facto reference implementation (Adobe Acrobat) which, if your implementation does not match exactly, users will think your implementation is broken.

There isn't such an implementation for SVG.

0x1ch 12/19/2025||||
We live in a world where Adobe set the standard, and anything that didn't render like Adobe was considered "incorrect".
eek2121 12/19/2025|||
You definitely don't understand PDFs, let alone SVGs.

PDFs can also contain scripts. Many applications have had issues rendering PDFs.

Don't get me wrong, the folks creating the SVG standard should've used their heads. This is like the 5th time (that I am aware of) this type of issue has happened, (and at least 3 of them were Adobe). Allowing executable code in an image/page format shouldn't be a thing.

silverwind 12/19/2025||||
SVG can for example contain text elements rendered with a font. If the font is not available it will render in a different one. The issue can be avoided by turning text elements into paths, but not all SVGs do that.
GoblinSlayer 12/19/2025||
Also text zoom.
Karliss 12/19/2025||||
More like HTML and getting different browsers to render pixel perfectly identical result (which they don't) including text layout and shaping. Where different browser don't mean just Chrome, Firefox, Safari but also also IE6 and CLI based browsers like Lynx.

PDFs at least usually embed the used subset of fonts and contain explicit placement of each glyph. Which is also why editing or parsing text in PDFs is problematic. Although it also has many variations of Standard and countless Adobe exclusive extensions.

Even when you have exactly the same font text shaping is tricky. And with SVGs lack of ability to embed fonts, files which unintentionally reference system font or a generic font aren't uncommon. And when you don't have the same font, it's very likely that any carefully placed text on top of diagram will be more or less misplaced, badly wrap or even copletely disappear due to lack of space. Because there is 0 consistency between the metrics across different fonts.

The situation with specification is also not great. Just SVG 1.1 defines certain official subsets, but in practice many software pick whatever is more convenient for them.

SVG 2.0 specification has been in limbo for years although seems like recently the relevant working group has resumed discussions. Browser vendors are pushing towards synchronizing certain aspects of it with HTML adjacent standards which would make fully supporting it outside browsers even more problematic. It's not just polishing little details many major parts that were in earlier drafts are getting removed, reworked or put on backlog.

There are features which are impractical to implement or you don't want to implement outside major web browsers that have proper sandboxing system (and even that's not enough once uploads get involved) like CSS, Javascript, external resource access across different security contexts.

There are multiple different parties involved with different priorities and different threshold for what features are sane to include:

- SVG as scalable image format for icons and other UI elements in (non browser based) GUI frameworks -> anything more complicated than colored shapes/strokes can problematic

- SVG as document format for Desktop vector graphic editors (mostly Inkscape) -> the users expect feature parity with other software like Adobe Illustrator or Affinity designer

- SVG in Browsers -> get certain parts of SVG features for free by treating it like weird variation of HTML because they already have CSS and Javascript functionality

- SVG as 2d vector format for CAD and CNC use cases (including vinyl cutters, laser cutters, engravers ...) -> rarely support anything beyond shapes of basic paths

Beside the obviously problematic features like CSS, Javascript and animations, stuff like raster filter effects, clipping, text rendering, and certain resource references are also inconsistently supported.

From Inkscape unless you explicitly export as plain 1.1 compatible SVG you will likely get an SVG with some cherry picked SVG2 features and a bunch of Inkscape specific annotations. It tries to implement any extra features in standard compatible way so that in theory if you ignore all the inkscape namespaced properties you would loose some of editing functionality but you would still get the same result. In practice same of SVG renderers can't even do that and the specification for SVG2 not being finalized doesn't help. And if you export as 1.1 plain SVG some features either lack good backwards compatibility converters or they are implemented as JavaScript making files incompatible with anything except browsers including Inkscape itself.

Just recently Gnome announced working on new SVG render. But everything points that they are planning to implement only the things they need for the icons they draw themselves and official Adwaita theme and nothing more.

And that's not even considering the madness of full XML specification/feature set itself. Certain parts of it just asking for security problems. At least in recent years some XML parsers have started to have safer defaults disabling or not supporting that nonsense. But when you encounter an SVG with such XML whose fault is it? SVG renderer for intentionally not enabling insane XML features or the person who hand crafted the SVG using them.

0x0203 12/18/2025||||
Even PDFs don't always render the same from one platform to another. I've mostly seen it due to missing fonts.
Blackthorn 12/19/2025|||
Most renderers don't implement the full spec.
VBprogrammer 12/19/2025|||
Yeah, I spent a bit of time trying to figure out some masking issues with a file I created in Inkscape but which chrome would butcher. Turned out to be opacity on a mask layer or something.
HPsquared 12/18/2025|||
Could there be a limited format that disables scripting? Like in Excel: xlsx files have no macros, but xlsm (and the old xls) can contain macros.
IgorPartola 12/19/2025|||
But how else would we revisit all the security bugs of Flash/Macromedia?
username223 12/18/2025|||
It's wild how often we rediscover that executing untrusted code leads to decades of whack-a-mole security. Excel/Word plus macros, HTML plus JavaScript, SVG plus JavaScript, ...
eastbound 12/18/2025||
It’s wild how often specs are ok for 9 versions, and then at version 10, standard bodies decide to transform them into a trojan firehose.

It’s so regular like clockwork that it has to be a nation state doing this to us.

moss_dog 12/18/2025||
Any notable examples you can share?
kevin_thibedeau 12/18/2025||
PDF was purposely a non-Turing adaptation of PostScript. Then they added JavaScript support.
nightski 12/18/2025|||
Does it need to be as complicated as a new format? Or would it be enough to not allow any scripting in the provided SVGs (or stripping it out). I can't imagine there are that many SVGs out there which take advantage of the feature.
FeepingCreature 12/18/2025|||
If only there was a widely used vector format that had script support and also decades of work on maintaining a battle-tested security layer around it with regular updates on a faster release cycle than your browser. That'd be crazy. Sure would suck if we killed it because we didn't want to bother maintaining it anymore.

(Yes I'm still salty about Flash.)

JoshTriplett 12/18/2025|||
> because we didn't want to bother maintaining it anymore

That wasn't the only reason. Flash was also proprietary, and opaque, and single-vendor, among many other problems with it.

ajross 12/18/2025||||
Uh... Flash was a genuine firehose of security flaws. I mean, yeah, they patched them. So "battle tested security layer" isn't wrong in a technical sense. But, yikes, no.
acheron 12/18/2025||
The Flash revisionism I see around here occasionally is bizarre.

No, Flash was terrible and killing it was good.

Blackthorn 12/19/2025|||
There is artistically no equivalent to Flash ever since it died. Nothing else has allowed someone with artistic skills but no programming skills to create animations and games to the same degree and with the same ease.
johnny22 12/19/2025|||
what is missing was a replacement for the flash editor itself, not the format.
ajross 12/19/2025|||
I'd say Roblox is absolutely filling that market need. And as mentioned elsewhere, the "animations and games" demographic has moved on in the intervening decades to social media, and tools like CapCut make creating online content easier than it ever has been.

Honestly I think a lot of the Flash mania is just middle aged nerds fondly remembering their youth. The actual tool was a flash in the pan, and part of a much more complicated history of online content production. And the world is doing just fine without it.

RulerOf 12/19/2025||||
It was terrible from a security POV, but the tooling was superb.

I remember my teenage friends creating things with flash in a way that doesn't happen on the modern web.

ajross 12/19/2025||
Sure, but that's because the media and forums change, not so much a point about tool capability. The equivalent of teenaged geeks hacking on flash games today is influencer wannabes editting trends in CapCut. If anything content production is far more accessible now than in the 90's.
FeepingCreature 12/19/2025|||
I think it depends on whether you see Flash as competing with webvideo or with downloadable executables.
lambdaone 12/18/2025|||
SVG without <script> would do just fine.
naasking 12/19/2025||
SVG also supports event attributes, so you should probably strip those too.
Pxtl 12/19/2025|||
What we got was html for vector graphics and what we wanted was jpeg for vector graphics.
Gander5739 12/18/2025|||
Wikipedia, which allows uploading media, deals with this by rendering svgs on the server side.
zahlman 12/19/2025|||
Yeah, it's still insane to me that the SVG can contain scripts. Wholly unnecessary; the DOM subtree it defines could be manipulated by external scripts just fine.

Anyway, I just set `svg.disabled` in Firefox. Scary world out there.

zahlman 12/20/2025||
Update: this breaks quite a few things. It seems legitimate SVGs are used more often for UI icons than random diagrams and such. I suppose I shouldn't be surprised. I'll have to rethink this.
css_apologist 12/18/2025|||
is santizing SVGs hard, or just everyone forgets they can contain js?
rslashuser 12/18/2025|||
I gather from the HN discussion that it's not simple to disable scripting in an SVG, in retrospect a tragically missing feature.

I guess the next step is to propose a simple "noscripting" attribute, which if present in the root of the SVG doc inhibits all scripting by conforming renderers. Then the renderer layer at runtime could also take a noscripting option, so the rendering context could force it if appropriate. Surely someone at HN is on this committee, so see what you can do!

Edit: thinking about it a little more - maybe it's best to just require noscripting as a parameter to the rendering function. Then the browsers can have a corresponding checkbox to control SVG scripting and that's it.

staticassertion 12/19/2025|||
Disabling script execution in svgs is very easy, it's just also easy to not realize you're about to embed an svg. `<img src="evil.svg">` will not execute scripts, a bit like your "noscripting" attribute except it's already around and works. Content Security Policy will prevent execution as well, you should be setting one for image endpoints that blocks scripts.

Sanitizing is hard to get right by comparison (svgs can reference other svgs) but it's still a good idea.

rslashuser 12/19/2025||
I had the impression from elsewhere in this thread that loading the svg in some other way, then you are not protected. This makes a no-brainer "don't run these ever" option in the browser seem appealing.
zahlman 12/19/2025||
> This makes a no-brainer "don't run these ever" option in the browser seem appealing.

Firefox has this: svg.disabled in about:config. It doesn't seem to be properly documented, and might cause other problems for the developer (I found it accidentally, and a more deliberate search turns up mainly bug tracker entries.)

css_apologist 12/18/2025|||
its common to santize html string to parse it and remove/error on script tags (and other possible vulnerabilities)

i wonder do people not do this with svgs?

AmbroseBierce 12/18/2025|||
User name checks out.
coolcoder613 12/19/2025||
I believe the username is from the AI simulation of HN in 10 years.
SV_BubbleTime 12/18/2025|||
> On one hand, the animations and entire interactive demos and even games in a single SVG are cool. But on the other hand

Didn’t we do this already with Flash? Why would this lesson not have stuck?

hoppp 12/18/2025|||
I agree, when animating SVGs I never put the js inside them so having the ability embed it is just dangerious I think
msie 12/18/2025|||
Wow, I learned one thing today!
culi 12/18/2025|||
Do other vector formats have the same vulnerabilities?
fainpul 12/18/2025|||
"The script doesn't run unless the file is directly opened (you can't run scripts from (<img src="/image.svg">)."
kevin_thibedeau 12/18/2025||
It will run if its in an <object> tag.
amonith 12/19/2025||
So if you're directly embedding the thing. This is a somewhat rare use case, should not be banned almost anywhere...
aydyn 12/18/2025||
There is: PDF. You may not like it or adobe, but its there and widely supported.
Shared404 12/18/2025|||
PDF also has script support unfortunately.
mikkupikku 12/18/2025|||
That's apparently how 4chan got hacked a while back. They were letting users upload PDFs and were using ghostscript to generate thumbnails. From what I understand, the hackers uploaded a PDF which contained PostScript which exploited a ghostscript bug.
diath 12/18/2025||
Yes but the primary issue was that 4chan was using over a decade old version of the library that contained a vulnerability first disclosed in 2012: https://nvd.nist.gov/vuln/detail/CVE-2012-4405
jonahx 12/18/2025|||
Does that mean that opening arbitrary pdfs on your laptop is unsafe?
Sohcahtoa82 12/18/2025|||
Let me put it this way...

In one of my penetration testing training classes, in one of the lessons, we generated a malicious PDF file that would give us a shell when the victim opened it in Adobe.

Granted, it relied on a specific bug in the JavaScript engine of Adobe Reader, so unless they're using a version that's 15 years old, it wouldn't work today, but you can't be too cautious. 0-days can always exist.

bmacho 12/18/2025|||
Yes, opening random pdfs especially in random and old pdf viewers is not a good idea.

If you must open a possibly infected pdf, then do it in browser, pdf.js is considered mostly safe, and updated.

rvnx 12/19/2025||
Use the PDF to JPG online services, convenient and you still get your result without having to deal with any sandbox
bpt3 12/19/2025||
Except of course that you're sharing the contents of that PDF with a random online service.
rvnx 12/19/2025||
True, I just considered that once you handle a PDF with so much care like if it was poisoned, it's perhaps better to send this poison to someone else to handle.
anthk 12/18/2025|||
Better a DJVU file generated at a high DPI.
padjo 12/18/2025||
Seems like such a tiny amount of money for a bug that can be used to completely own your customers accounts. Also not much excuse for xss these days.
tptacek 12/18/2025||
This comes up on every story about bug bounties. There is in general no market at all for XSS vulnerabilities. That might be different for Twitter, Facebook, Instagram, and TikTok, because of the possibility of monetizing a single strike across a whole huge social network, and there's maybe a bank-shot argument for Discord, but you really have to do a lot of work to generate the monetization story for any of those.

The vulnerabilities that command real dollars all have half-lives, and can't be fixed with a single cluster of prod deploys by the victims.

jijijijij 12/18/2025|||
If a $500 drone is coming for your $100M factory, the price limit for defense considerations isn't $500.

In the end, you are trying to encourage people not to fuck with your shit, instead of playing economic games. Especially with a bunch of teenagers who wouldn't even be fully criminally liable for doing something funny. $4K isn't much today, even for a teenager. Thanks to stupid AI shit like Mintlify, that's like worth 2GB of RAM or something.

It's not just compensation, it's a gesture. And really bad PR.

tptacek 12/18/2025||
That's not how any of this works. A price for a vulnerability tracking the worst-case outcome of that vulnerability isn't a bounty or a market-clearing price; it's a shakedown fee. Meanwhile: the actual market-clearing price of an XSS vulnerability is very low (in most cases, it doesn't exist at all) because there aren't existing business processes those vulnerabilities drop seamlessly into; they're all situational and time-sensitive.
jonahx 12/18/2025|||
> the actual market-clearing price of an XSS vulnerability is very low (in most cases, it doesn't exist at all) because there aren't existing business processes those vulnerabilities drop seamlessly into; they're all situational and time-sensitive.

Could you elaborate on this? I don't fully understand the shorthand here.

tptacek 12/18/2025||
I'm happy to answer questions but the only thing I could think to respond with here is just a restatement of what I said. I was terse; which part do you want me to expand on? Sorry about that!
jonahx 12/18/2025||
> because there aren't existing business processes those vulnerabilities drop seamlessly into; they're all situational and time-sensitive.

what's an example of an existing business process that would make them valuable, just in theory? why do they not exist for xss vulns? why, and in what sense, are they only situational and time-sensitive?

i know you're an expert in this field. i'm not doubting the assertions just trying to understand them better. if i understand you're argument correctly, you're not doubting that the vuln found here could be damaging, only doubting that it could make money for an adversary willing to exploit it?

tptacek 12/18/2025|||
I can't think of a business process that accepts and monetizes pin-compatible XSS vulnerabilities.

But for RCE, there's lots of them! RCE vulnerabilities slot into CNE implants, botnets, ransomware rigs, and organized identity theft.

The key thing here is that these businesses already exist. There are already people in the market for the vulnerabilities. If you just imagine a new business driven by XSS vulnerabilities, that doesn't create customers, any more than imagining a new kind of cloud service instantly gets you funded for one.

jonahx 12/19/2025|||
Thank you, makes a lot of sense.

I wonder what you think of this, re: the disparity between the economics you just laid out and the "companies are such fkn misers!" comments that always arise in these threads on bounty payouts...

I've seen first hand how companies devalue investment in security -- after all, it's an insurance policy whose main beneficiaries are their customers. Sure it's also reputational insurance in theory, but what is that compared with showing more profit this quarter, or using the money for growth if you're a startup, etc. Basically, the economic incentives are to foist the risks onto your customers and gamble that a huge incident won't sink you.

I wonder if that background calculus -- which is broadly accurate, imo -- is what rankles people about the low bounty rewards, especially from companies that could afford more?

tptacek 12/19/2025||
The premise that "fucking companies are misers" operate on that I don't share is that vulnerabilities are finite and that, in the general case, there's an existential cost to not identifying and fixing them. From decades of vulnerability research work, including (over the past 5 years) as a buyer rather than a seller of that work: put 2 different teams on a project, get 2 different sets of vulnerabilities, with maybe 30-50% overlap. Keep doing that; you'll keep finding stuff.

Seen through that light, bug bounty programs are engineering services, not a security control. A thing generalist developers definitely don't get about high-end bug bounty programs is that they are more about focusing internal resources than they are about generating any particular set of bugs. They're a way of prioritizing triage and hardening work, driven by external incentives.

The idea that Discord is, like, eliminating their XSS risk by bidding for XSS vulnerabilities from bounty hunters; I mean, just, obviously no, right?

zahlman 12/19/2025|||
How does stealing someone social media accounts not slot into "organized identity theft"?

... actually: how is XSS not a form of RCE? The script is code; it's executed on the victim's machine; it arrives remotely from the untrusted, attacker-controlled source.

And with the legitimate first-party's permissions and access, at that. It has access to things within the browser's sandbox that it probably really shouldn't. Imagine if a bank had used Mintlify or something similar to implement a customer service portal, for example.

tptacek 12/19/2025||
You're misreading me. It's organized identity theft driven by pin-compatible RCE exploits. Is there already an identity theft ring powered by Mintlify exploits? No? Then it doesn't matter.

The subtlety here is the difference between people using an exploit (certainly they can) and people who buy exploits for serious money.

jgeralnik 12/18/2025|||
A remote code execution bug in ios is valuable - it may take a long time to detect exploitation (potentially years if used carefully), and even after being discovered there is a long tail of devices that take time to update (although less so than on android, or linux run on embedded devices that can’t be updated) That’s why it’s worth millions on the black market and apple will pay you $2 million dollars for it

An XSS is much harder to exploit quietly (the server can log everything), and can be closed immediately 100% with no long tail. At the push of an update the vulnerability is now worth zero. Someone paying to purchase an XSS is probably intending to use it once (with a large blast radius) and get as much as they can from it in the time until it is closed (hours? maybe days?)

jijijijij 12/18/2025|||
> That's not how any of this works.

Yes, evidently not.

Just because on average the intelligence agencies or ransom ware distributors wouldn't pay big bucks for XSS on Zerodium etc. doesn't mean that's setting the fair, or wise price for disclosure. Every bug bounty program is mostly PR mitigation. It's bad PR if you underpay for a disclosed vulnerability, which may have ended your business, considering the price of security audits/practices you cheaped out on. I mean, most bug bounty programs are actually paid by scope, not market price for technically comparable exploits. If you found an XSS vulnerability in an Apple service with this scope, I bet you would have been paid more than 4k.

tptacek 12/18/2025||
Nobody is buying anything on "Zerodium".
jijijijij 12/18/2025||
I wasn't aware they are gone. It's not my game, replace with whatever shady exploit trader/market out there.
tptacek 12/18/2025||
I do not in fact think you would make a lot more than $4000, or even $4000 in the first place, for an Apple XSS bug, unless it was extraordinarily situationally powerful (for instance, a first-stage for a clean, direct RCE). Bounty prices have nothing at all to do with the worst-case damage a motivated actor could cause with a vulnerability.
jijijijij 12/18/2025||
https://security.apple.com/bounty/categories/

The lowest tier is $5k. XSS up to $40k. I think we're talking exfiltration of dev credentials...

tptacek 12/18/2025||
Nice, I hadn't seen that. Well, there you go: the absolute most you're going to make for the absolute worst-case XSS bug at the largest software firm in the world.
greggh 12/19/2025|||
Right, but Eva found an RCE and only got $5,000.
tptacek 12/19/2025||
An RCE in what? Nobody's buying your Discord RCE.
da_grift_shift 12/18/2025||
>Also not much excuse for xss these days.

XSS is not dead, and the web platforms mitigations (setHTML, Trusted Types) are not a panacea. CSP helps but is often configured poorly.

So, this kind of widespread XSS in a vulnerable third party component is indeed concerning.

For another example, there have been two reflected XSS vulns found in Anubis this year, putting any website that deploys it and doesn't patch at risk of JS execution on their origin.

Audit your third-party dependencies!

https://github.com/TecharoHQ/anubis/security/advisories/GHSA...

https://github.com/TecharoHQ/anubis/security/advisories/GHSA...

azemetre 12/18/2025||
Is it really fair to compare an open source project that desperately wants only $60k a year to hire a dev with companies that have collectively raised over billions of dollars in funding?
rafram 12/18/2025|||
I think it’s very fair. Anubis generated a lot of buzz in tech communities like this one, and developers pushed it to production without taking a serious look at what it’s doing on their server. It’s a very flawed piece of software that doesn’t even do a good job at the task it’s meant for (don’t forget that it doesn’t touch any request without “Mozilla” in the UA). If some security criticism gets people to uninstall it, good.
noirscape 12/18/2025||||
I'd say it's probably worse in terms of scope. The audience for some AI-powered documentation platform will ultimately be fairly small (mostly corporations).

Anubis is promoting itself as a sort of Cloudflare-esque service to mitigate AI scraping. They also aren't just an open source project relying on gracious donations, there's a paid whitelabel version of the project.

If anything, Anubis probably should be held to a higher standard, given many more vulnerable people (as in, vulnerable against having XSS on their site cause significant issues with having to fish their site out of spam filters and/or bandwidth exhaustion hitting their wallet) are reliant on it compared to big corporations. Same reason that a bug in some random GitHub project somewhere probably has an impact of near zero, but a critical security bug in nginx means that there's shit on the fan. When you write software that has a massive audience, you're going to have to be held to higher standards (if not legally, at least socially).

Not that Anubis' handling of this seems to be bad or anything; both XSS attacks were mitigated, but "won't somebody think of the poor FOSS project" isn't really the right answer here.

azemetre 12/18/2025||
I don't think it's fair to hold them to the same, or higher standard. at all this is literally a project being maintained by one individual. I'm sure if they were given $5 million in seed money they could probably provide 1000x value for the industry writ large if they could hire a dedicated team for the product like all those other companies with 100,000x the budget.
naasking 12/19/2025|||
Seems fair. XSS is a confused deputy attack, a type of vulnerability known since the 1980s. That we keep reinventing it in every new medium is frankly embarassing.
0xbadcafebee 12/18/2025||
How these companies don't hire kids like Daniel for pennies on the dollar and have him attack their stacks on a loop baffles me. Pay the kid $50k/yr (part time, he still needs to go to school) to constantly probe your crappy stacks. Within a year or two you'll have the most goddamn secure company on the internet - and no public vulns to embarrass you.
wiether 12/18/2025||
That's a bit simplistic.

If you sign a contract with a "hacker", then you are expecting results. Otherwise how do you decide to renew the contract next year? How do you decide to raise it next year? What if, during this contract, a vulnerability that this individual didn't found is exploited? You get rid of them?

So you're putting pressure on a person who is a researcher, not a producer. Which is wrong.

And also there's the scale. Sure, here you have one guy who exploited a vulnerability. But how long it took them to get there? There's probably dozens of vulnerabilities yet to be exploited, requiring skills that differ so much from the ones used by this person that they won't find them. Even if you pay them for a full-time position.

Whereas, if you set up a bug bounty program, you are basically crowdsourcing your vulnerabilities: not only you probably have thousands of people actively trying to exploit vulnerabilities in your system, but also, you only give money to the ones that do manage to exploit one. You're only paying on result.

Obviously, if the reward is not big enough, they could be tempted to sell them to someone else or use them themselves. But the risk is here no matter how you decide to handle this topic.

tptacek 12/19/2025|||
Just going to say here that people routinely engage pentest firms, several times annually, for roughly that sum of money, hoping but not expecting game-over vulnerabilities (and, from bitter experience as a buyer rather than a seller of those services over the last 5 years --- "no game-over vulnerabilities" is a very common outcome!)
wiether 12/19/2025|||
I completely agree!

But hiring a pentest firm is completely different than giving $50k a year to a guy, no questions asked.

The pentest firm is generally providing the whole package, from doing the actual pentest, with tools and workers of various experience and skill sets, giving you extended reports on what they did and the outcome, to providing guidance on how to fix their findings, how to make the necessary cultural changes to harden your apps, and also how to communicate that you have passed their audit.

You won't have all of that if you give free roam to a guy to _do what they do_.

This idea is more similar to patronage, which, imho, is a great idea, no matter the domain (arts or tech), but I doubt that there any company here that is willing to go this way.

Even the company that supposedly do actual patronage today are going to look at their ROI and stop as soon as they don't see the figures they're expecting.

tptacek 12/20/2025||
Don't get me wrong, I'm not saying it's dumb to think about retaining a talented teenager on a contract.
rkomorn 12/19/2025|||
> from bitter experience as a buyer rather than a seller of those services over the last 5 years --- "no game-over vulnerabilities" is a very common outcome!

Why bitter? Did they miss some?

Otherwise, isn't that the goal to begin with? Shouldn't you be proud instead?

tptacek 12/19/2025||
Every pentest misses stuff. That's kind of the point I'm making. But yeah: as someone with a software security background, when you contract a test, you want them to find stuff!
sammy2255 12/18/2025||||
They've already proved themselves as competent. $50k a year to a billion dollar company is nothing. Even if they find 0 vulnerabilities a year it's still worth it to them
tptacek 12/19/2025|||
I directionally agree with you but we could go another 20 comments deep on exactly what the purpose of an external pentest or red-team exercise is and how it might not match up perfectly with what an amateur web hacker is currently doing. But like: yeah, they could get into that business, at least until AI eats it.
wiether 12/19/2025|||
So now they found a vulnerability, the company should pay them $50k a year until they retire because they proved themselves competent?
sammy2255 12/19/2025||
Yes?
staticassertion 12/19/2025|||
There are a lot of ways to monetize a security researcher. Publishing research, even "we failed to perform a full exploit", is a huge recruitment tool and brand awareness tool.
bink 12/18/2025|||
It's not quite that simple. I don't think most bug bounty participants want a full-time job. But even more-so in my experience they are not security generalists. You can hire one person who is good at finding obscure XSS vulns, another that's good at exploiting cloud privilege escalation in IAM role definitions, another that's good at shell or archive exploits. If you look at profiles on H1 you'll see most good hackers specialize in specific types of findings.
philipwhiuk 12/19/2025|||
I doubt it.

Just because he found one vulnerability at one vendor used by Discord doesn't mean he'll find all the vulnerabilities that exist at Discord or indeed any of them.

integralid 12/19/2025||
TFA:

>Discord is one of my favorite places to hunt for vulnerabilities since I'm very familiar with their API and platform. I'm at the top of their bug bounty leaderboard having reported nearly 100 vulnerabilities over the last few years. After you've gone through every feature at least 10 times, it gets boring.

Aachen 12/19/2025||
That doesn't specify how many bugs there existed in the Discord codebase throughout the time where this person was active. Only once you know that, can you say whether they found a significant proportion relative to the effort they've spent and would spend as a part-time employee. That other people still find things also suggests that the statement above ("just hire him and you're secure") might have been a bit simplistic
reincarnate0x14 12/19/2025|||
Having been adjacent to this for years, it's because it's a cost center and not attached to the bonus of any product or program manager. Every now and then we'll get an advocate for security/integrity at a company but the effort lives and leaves with them.

Microsoft, after getting beat up over this for decades, is still horrible at it. In my area they're have been enforced regulations for years but they're written by the industry itself and infected with compliance managers and thus result in wastes of effort that makes compliance managers that came over from HR and legal happy with their eternal job security and minimal hard work.

Until some heavy handed top down regulation, written by people who understand the nature of ongoing security and software and embedded lifecycles, it's going to stay like this. Most existing supply chain regulation I've seen ends up saying "vet your vendors" and gives minimal practical guidance of how to actually do that. Likelihood of some really good law coming out of the current US administration and business climate is left as a comedy for the reader.

fergie 12/19/2025|||
I feel like the "I'm a 16 year old high school senior" thing is some kind of social engineering- his knowledge seems a bit too broad.

But who knows.

Alex-Programs 12/19/2025|||
There are plenty of competent 16 year olds.
gavinray 12/19/2025||
I just read a story about a 13-year-old awarded a Ph. D at a prestigious university.

Human intelligence/aptitude has such extreme distributions it's almost unthinkable.

Rapzid 12/19/2025|||
Who knows indeed.

It's easier than ever to pretend you know more than you do on the internet these days..

Not saying that's the case here, but that's the world we live in now.

makeitdouble 12/19/2025|||
I wonder if this analogy could work: if some random visitor pointed out your storage room's key is nearly broken and anybody could come in now and steal your store's stock. You'd be thankful, but would you hire them to come from time to time to check if they have any other insight ? Probably not ?

If you really saw a recurring security risk you'd have many other better use of your money.

joenot443 12/19/2025|||
Apple hired George Hotz (geohot) after he wrote the old 2010s iOS jailbreaks.

It wouldn't surprise me if he's in this thread - curious what his thoughts would be.

zwnow 12/18/2025|||
While I would love that for the kid I dont think these companies care about security at all.
mpeg 12/18/2025||
I think that's unfair to say about a company that pays bug bounties at all.

A lot of other companies would have ignored the email for weeks or threatened legal action.

zwnow 12/19/2025||
Its cheaper to pay bug bounties than to hire a security expert or legal costs
stainablesteel 12/19/2025|||
just wanted to disagree with anyone who thinks someone like this needs to go to school

no, he needs to make his own agency

kitsune1 12/19/2025||
[dead]
dfbrown 12/18/2025||
Their collaborator's report includes a more significant issue, an RCE on a mintlify server: https://kibty.town/blog/mintlify/
Illniyar 12/18/2025||
Nice discovery and writeup. Let alone for a 16 yo!.

I've never heard an XSS vulnerability described as a supply-chain attack before though, usually that one is reserved for package managers malicious scripts or companies putting backdoors in hardware.

kenjackson 12/18/2025||
I think you can view it as supply chain as the supply chain is about attacking resources used to infiltrate downstream (or is it upstream? I get which direction I should think this flows).

As an end user you can't really mitigate this as the attack happens in the supply chain (Mintlify) and by the time it gets to you it is basically opaque. It's like getting a signed malicious binary. It looks good to you and the trust model (the browser's origin model) seems to indicate all is fine (like the signing on the binary). But because earlier in the supply chain they made a mistake, you are now at risk. Its basically moving an XSS up a level into the "supply chain".

Aachen 12/19/2025||
A supply chain attack attacks the supply chain

This makes use of a vulnerability in a dependency. If they had recommended, suggested, or pushed this purposefully vulnerable code to the dependency, then waited for a downstream (such as Discord) to pull the update and run the vulnerable code, then they would have completed a supply chain attack

The whole title is bait. Nobody would have heard of the dependency, so they don't even mention it, just call it "a supply chain" and drop four big other names that you have heard of to make it sexy. One of them was actually involved that I can tell from the post, that one is somewhat defensible. They might as well have written in the title that they've hacked the pentagon, if someone in there uses X and X had this vulnerable dependency, without X or the pentagon ever being contacted or involved or attacked

kenjackson 12/19/2025||
It does attack the supply chain. It attacks the provider of documentation. It's an attack on the documentation supply chain.

It would be like if you could provide a Windows Update link that went to Windows Update, but you could specify Windows Update to retrieve files from some other share that the malicious actor had control of. It's the same thing, except rather than it being a binary rather it is documentation.

bink 12/18/2025||
I think that's misuse of the term as well, but like you said they are only 16.
marisen 12/18/2025||
Given this (including the linked writeup on the mintlify RCE), after the React RCE, if think it should be pretty obvious that

1. content security policies should always be used to prevent such scripts (here they would prevent execution of scripts from the SVG)

2. The JavaScript ecosystem should be making ` --disallow-code-generation-from-strings` a default recommendation when running NodeJS on the server.

Vercel (and other nodejs as a service providers) should warn customers that don't use CSP and `--disallow-code-generation-from-strings` that their settings should be improved.

There are a bunch of other NodeJS flags that maybe you should look into too: https://sgued.fr/blog/react-rce/#node-js-mitigations

bri3d 12/18/2025||
Proxying from the "hot" domain (with user credentials) to a third party service is always going to be an awful idea. Why not just CNAME Mintlify to dev-docs.discord.com or something?

This is also why an `app.` or even better `tenant.` subdomain is always a good idea; it limits the blast radius of mistakes like this.

gkoberger 12/18/2025||
I run a product similar to Mintlify.

We've made different product decisions than them. We don't support this, nor do we request access to codebases for Git sync. Both are security issues waiting to happen, no matter how much customers want them.

The reason people want it, though, is for SEO: whether it's true or outdated voodoo, almost everyone believes having their documentation on a subdomain hurts the parent domain. Google says it's not true, SEO experts say it is.

I wish Mintlify the best here – it's stressful to let customers down like this.

Dma54rhs 12/18/2025|||
What makes you say that Google claims it's not true? Google claims subdomains are completely two different domains and you'll lose all the linking/page rank stuff according to their own docs regarding SEO. Some SEO gurus claim it's not so black and white but no one knows for sure. The data does show having docs on subdomain is more harmful to your SEO if you get linked to then a lot.
gkoberger 12/18/2025||
Here's the argument for/against it: https://www.searchenginejournal.com/ranking-factors/subdomai...

I think the answer likely is quite nuanced, for what it's worth.

omneity 12/18/2025|||
To my knowledge it's not as much hurting the parent domain as having two separate "worlds". Your docs which are likely to receive higher traffic will stop contributing any SEO juice to your main website.
odensc 12/18/2025|||
Yep - this is the core issue that made the vulnerability so bad. And if you use a subdomain for a third-party service, make sure your main app auth cookies are scoped to host-only. Better yet, use a completely different domain like you would for user-generated content (e.g. discorddocs.com).
pverheggen 12/18/2025||
I think the reason companies do this for doc sites is so they can substitute your real credentials into code snippets with "YOUR_API_KEY". Seems like a poor tradeoff given the security downside.
multisport 12/18/2025|
decided to make a new account to post:

Mintlify security is the worse I have even encountered in a modern SaaS company.

They will leak your data, code, assets, etc. They will know they did this. You will tell them, they will acknowledge that they knew it happened, and didn't tell you.

Your docs site will go down, and you will need to page their engineers to tell them its down. This will be a surprise to them.

arpinum 12/18/2025||
Yes, they were sloppy with GitHub credentials and their response was inadequate. Glad we migrated away from them.
fazkan 12/19/2025||
where did you migrate away to?
hunvreus 12/19/2025||
Absolute self-promotion: https://github.com/hunvreus/reallysimpledocs
promiseofbeans 12/19/2025||
Astro’s starlight docs generator/template is quite nice as well: https://starlight.astro.build/
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