fix(oidc) :: compare logout in constant time - #1423
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Before verification compared the HMACs with an slice comparison. `Mac::verify_slice` removes the base64-encoding and decoding.
81reap
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September 2, 2026 02:43
lovasoa
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September 2, 2026 21:26
lovasoa
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Sep 2, 2026
lovasoa
marked this pull request as ready for review
September 2, 2026 21:28
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This was referenced Sep 2, 2026
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Logout URLs are signed with an HMAC over the redirect URI so that an attacker can't forge a logout URL. Verification compared the tags with
!=, which lowers to amemcmpand leaks the leading correct bytes from the response time.Mac::verify_slicecompares every byte before deciding.We also end up dropping a base64 encode/decode round trip and a now unreachable "Failed to decode expected signature" branch.