Signature Malleability in jose Library Impacts Token Validation

CVE-2026-65632

What is CVE-2026-65632?

The jose library is vulnerable to a signature malleability issue due to its handling of ECDSA signatures. When verifying these signatures, the library does not enforce the fixed length specified by RFC 7518 §3.4. Instead, it splits the signature in half based on its current byte length, allowing attackers to prepend leading zero bytes to the signature's R and S halves. This results in multiple distinct signature strings that can verify against the same key, undermining security controls expecting unique signatures, such as token revocation and cache mechanisms. This vulnerability specifically affects versions of the jose library from 1.0.0 up to, but not including, 1.11.13.

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