{"id":"EEF-CVE-2026-65632","summary":"ECDSA signature length is not validated in jose, allowing signature malleability","details":"## Summary\n\nThe `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 §3.4, and then decodes each half with `crypto:bytes_to_integer/1`, which ignores leading zero bytes.\n\nAs 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.\n\nThis issue affects jose: from 1.0.0 before 1.11.13.","aliases":["CVE-2026-65632","GHSA-44hw-rpw9-mwg4"],"modified":"2026-10-26T20:11:07.849428784Z","published":"2026-10-26T19:53:56.649Z","database_specific":{"cpe_ids":["cpe:2.3:a:potatosalad:jose:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-347"],"capec_ids":["CAPEC-475"]},"references":[{"type":"ADVISORY","url":"https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-44hw-rpw9-mwg4"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-65632.html"},{"type":"WEB","url":"https://github.com/potatosalad/erlang-jose/commit/a7746ecd4950f85a393136e449a91dac62b5c429"},{"type":"FIX","url":"https://github.com/potatosalad/erlang-jose/commit/72ce1866622b9329347dc52a94173ac0317bc9cf"},{"type":"PACKAGE","url":"https://hex.pm/packages/jose"}],"affected":[{"package":{"name":"jose","ecosystem":"Hex","purl":"pkg:hex/jose"},"ranges":[{"type":"SEMVER","events":[{"introduced":"1.0.0"},{"fixed":"1.11.13"}]}],"versions":["1.0.0","1.0.1","1.1.0","1.1.1","1.1.2","1.1.3","1.10.0","1.10.1","1.11.0","1.11.1","1.11.10","1.11.11","1.11.12","1.11.2","1.11.4","1.11.5","1.11.6","1.11.7","1.11.8","1.11.9","1.2.0","1.3.0","1.4.0","1.4.1","1.4.2","1.5.0","1.5.1","1.5.2","1.6.0","1.6.1","1.7.0","1.7.1","1.7.2","1.7.3","1.7.4","1.7.5","1.7.6","1.7.7","1.7.8","1.7.9","1.8.0","1.8.1","1.8.2","1.8.3","1.8.4","1.9.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-65632.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/potatosalad/erlang-jose","events":[{"introduced":"a7746ecd4950f85a393136e449a91dac62b5c429"},{"fixed":"72ce1866622b9329347dc52a94173ac0317bc9cf"}]}],"versions":["1.11.12","1.11.11","1.11.10","1.11.9","1.11.8","1.11.7","1.11.5","1.11.4","1.11.2","1.11.1","1.11.0","1.10.1","1.10.0","1.9.0","1.8.4","1.8.3","1.8.2","1.8.1","1.8.0","1.7.9","1.7.8","1.7.7","1.7.6","1.7.5","1.7.4","1.7.3","1.7.2","1.7.1","1.7.0","1.6.1","1.6.0","1.5.2","1.5.1","1.5.0","1.4.2","1.4.1","1.4.0","1.3.0","1.2.0","1.1.3","1.1.2","1.1.1","1.1.0","1.0.1","1.0.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-65632.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"REPORTER"},{"name":"Andrew Bennett","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}]}