The jose library accepts ECDSA (ES256, ES256K, ES384, and ES512) JWS signatures of a non-canonical length. When verifying an ECDSA signature, jose_jwk_kty_ec:verify/4 in src/jwk/jose_jwk_kty_ec.erl splits the raw signature in half by its actual byte length (split_binary(Signature, byte_size(Signature) div 2)) instead of enforcing the fixed length required by RFC 7518 ยง3.4, and then decodes each half with crypto:bytes_to_integer/1, which ignores leading zero bytes.
As a result, an attacker who holds one valid token can prepend leading zero bytes to each of the R and S halves to produce longer signatures that still split evenly and decode to the same (r, s) pair, so many distinct signature byte strings all verify against the same key (signature malleability). This does not allow forging new payloads or impersonating a signer, because the underlying (r, s) values are unchanged. It does defeat any security control that assumes a valid token or its signature is unique, such as token-revocation-by-hash, replay or idempotency caches, and deduplication logic.
This issue affects jose: from 1.0.0 before 1.11.13.
CVSS
No CVSS.
References
Configurations
No configuration.
History
26 Oct 2026, 20:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-10-26 20:17
Updated : 2026-10-27 15:00
NVD link : CVE-2026-65632
Mitre link : CVE-2026-65632
CVE.ORG link : CVE-2026-65632
JSON object : View
Products Affected
No product.
CWE
CWE-347
Improper Verification of Cryptographic Signature