Limit the effect of state cookie tampering - #147
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DanilChapovalov
previously approved these changes
Jul 10, 2026
This commit enhances the security and robustness of the state cookie by limiting what an attacker can achieve even if they manage to forge or tamper with the cookie. Note that we don't add any signature or digest right now, as that would be done by adding library dependencies that the downstream projects don't use right now (sha2 and hmac). This might be rivisited in the future. By storing the raw peer capabilities in the state cookie, we prevent an attacker from enabling extensions that the local socket didn't signal support for, limit the stream limits (incoming and outgoing) from what was originally announced, and also elimintate some duplication in capability parsing in the different methods to do connection handshakes. This defense-in-depth measure ensures that the state instantiated from a COOKIE ECHO strictly matches the parameters of the original INIT, and if an attacker tampers with it, the effects are very limited.
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DanilChapovalov
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Jul 10, 2026
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This commit enhances the security and robustness of the state cookie by limiting what an attacker can achieve even if they manage to forge or tamper with the cookie. Note that we don't add any signature or digest right now, as that would be done by adding library dependencies that the downstream projects don't use right now (sha2 and hmac). This might be rivisited in the future.
By storing the raw peer capabilities in the state cookie, we prevent an attacker from enabling extensions that the local socket didn't signal support for, limit the stream limits (incoming and outgoing) from what was originally announced, and also elimintate some duplication in capability parsing in the different methods to do connection handshakes.
This defense-in-depth measure ensures that the state instantiated from a COOKIE ECHO strictly matches the parameters of the original INIT, and if an attacker tampers with it, the effects are very limited.