AIKIDO-2026-959477
jwcrypto is vulnerable to Improper Verification of Cryptographic Signature
31
Low Risk
This Affects:
jwcryptoTL;DR
jwcrypto verifies a JSON Web Signature against a JWKSet by looking up the signer's key using the kid header parameter. When a JWS carries multiple signatures, the verification path reads kid from the overall jose_header instead of each signature's own checked headers, so a signature that declares kid only in an unprotected header, or a non-first signature in a multi-signature JWS, can resolve against the wrong key from the set. This key-confusion is limited to specific and uncommon multi-signature or unprotected-header kid usage with a JWKSet. The fix reads kid from each signature's own checked headers before performing the key lookup.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and you verify multi-signature JWS objects, or JWS signatures using an unprotected-header kid value, against a JWKSet.
Background info
jwcrypto is vulnerable to Improper Verification of Cryptographic Signature in versions 1.3 - 1.5.9.
How to fix this
Upgrade the jwcrypto library to the patch version.
Links
GitHub Release
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