R2S was a painful one, but Lachlan was a dream of a security researcher to partner with. Not just from a responsible disclosure POV, but things like hopping on multiple calls with Meta and our team to help us validate remediations. Thank you Lachlan for helping make the internet safer (and great job on figuring out this 'labyrinth' of a vulnerability)

I was really surprised when this hit, and I discovered the protocol was essentially undocumented / unspecified. I was trying to find indicators of compromise and that was made more difficult by the lack of documentation.

It was really helpful that they had coordinated with WAF providers like cloud flare ahead of disclosure to put rules in place though.

A great read. Sylvie's writeup is good too: https://sylvie.fyi/posts/react2shell/

>> Amazingly, despite being a weekend, the Meta team triaged, reproduced, and confirmed my submission in around 17 hours.

Incredible. Realize what you have done from start to finish (with confirmation) in < 24 hours.

Nice read!

I love the "we are so back" vs. "it's so over" graph. Defines so much of this type of work. "Wow? ... nah... WOW?! ... nah..."

Whoda thunkit that

- blurring the lines between client code and server code

- creating a brand new protocol for communication between trusted and untrusted actors

- and with all of that allow the protocol to serialize code and not just primitives

Would be a tremendously stupid idea. And for what? To lock developers further into the react ecosystem. What a shitshow react continues to be.

What a great write-up. Thanks for sharing how you found this fascinating vulnerability and exploit.

Haha, nice.

One correction: The link in "To be honest, I'm not even sure if I understand it, but it's on my GitHub." goes to the wrong file (01 instead of 00).