Don't de-establish a live session on an unauthenticated accept - #47
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Don't de-establish a live session on an unauthenticated accept#47jagerman wants to merge 1 commit into
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handle_session_accept reset _is_established/_outbound_tag before the parse/verify try block, with the intent that a failed accept triggers a fresh session init. But the "B" payload is a sealed (anonymous-sender) box, so an on-path party that knows the session tag could forge a malformed type-"a" handshake and force a live, established session back to unestablished (stalling outbound data until re-establishment) before the forged accept fails verification. Mutate no live session state until the remote's identity signature verifies. Keep the "reset to trigger a new init" behaviour, but only for failures *after* authentication (decapsulation / key derivation) -- a genuine-but-broken accept -- by moving the reset into an inner catch around the post-signature block. A forged/garbage accept now fails at or before the signature check and leaves the established session intact. The genuine restart-recovery path is unaffected: a restarted remote signs with its unchanged identity key and decapsulates with our pending ephemeral keys, so it lands on the success path as before. The deprecated 1.0 handle_session_accept_deprecated path is left as-is: its accept carries no signature to gate on, so it needs separate thought. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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handle_session_accept reset _is_established/_outbound_tag before the parse/verify try block, with the intent that a failed accept triggers a fresh session init. But the "B" payload is a sealed (anonymous-sender) box, so an on-path party that knows the session tag could forge a malformed type-"a" handshake and force a live, established session back to unestablished (stalling outbound data until re-establishment) before the forged accept fails verification.
Mutate no live session state until the remote's identity signature verifies. Keep the "reset to trigger a new init" behaviour, but only for failures after authentication (decapsulation / key derivation) -- a genuine-but-broken accept -- by moving the reset into an inner catch around the post-signature block. A forged/garbage accept now fails at or before the signature check and leaves the established session intact.
The genuine restart-recovery path is unaffected: a restarted remote signs with its unchanged identity key and decapsulates with our pending ephemeral keys, so it lands on the success path as before.
The deprecated 1.0 handle_session_accept_deprecated path is left as-is: its accept carries no signature to gate on, so it needs separate thought.
(This is adapted from the report and (not quite complete) fix for this issue in #44.)