{"id":"EEF-CVE-2026-65625","summary":"Attacker-controlled AES-GCM authentication tag length allows tag forgery in jose","details":"## Summary\n\nThe pure-Erlang AES-GCM fallback in `jose_jwa_aes` derives the number of verified authentication tag bits from the attacker-supplied tag itself. In the `{aes_gcm, Bits}` clause of `block_decrypt/4`, the incoming tag is guarded only by `is_binary/1`, with no check on its length. Verification in `gcm_block_decrypt/6` then computes `TBits = bit_size(T)` and compares only those bits of the real 128-bit tag. An attacker who controls a JWE token can truncate the authentication tag to as little as 8 bits, so only 8 bits are ever checked. This reduces forgery resistance from 2^-128 to 2^-8, and a forged ciphertext is reliably accepted as authentic within 256 attempts without knowledge of the key (an authentication tag forgery and integrity bypass). Supplying a tag longer than 128 bits instead causes a badmatch that crashes the decrypting process. The fallback is reached through the public JWE decryption path whenever AES-GCM is not provided by a native crypto NIF, for example on FIPS or stripped or older OTP builds.\n\nThis issue affects jose: from 1.2.0 before 1.11.13.\n\n## Workarounds\n\nEnsure the runtime provides a crypto provider with native AES-GCM support (a standard Erlang/OTP build linked against OpenSSL) so that JOSE dispatches AES-GCM to the native `crypto` NIF instead of the `jose_jwa_aes` fallback.\n\n## Configurations\n\nThis vulnerability is only exploitable when AES-GCM is handled by the pure-Erlang `jose_jwa_aes` fallback. That fallback is used on deployments where the Erlang/OTP `crypto` NIF does not expose native AES-GCM (for example FIPS builds, or stripped or older OTP releases). Deployments with a native AES-GCM crypto provider dispatch GCM through `crypto` and are not affected.","aliases":["CVE-2026-65625","GHSA-6gxw-6f7r-cjr6"],"modified":"2026-10-26T20:11:07.497402732Z","published":"2026-10-26T19:52:54.987Z","database_specific":{"cwe_ids":["CWE-354"],"capec_ids":["CAPEC-475"],"cpe_ids":["cpe:2.3:a:potatosalad:jose:*:*:*:*:*:*:*:*"]},"references":[{"type":"ADVISORY","url":"https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-6gxw-6f7r-cjr6"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-65625.html"},{"type":"WEB","url":"https://github.com/potatosalad/erlang-jose/commit/8848b172575fb7d7e1e2977e8ae0a21678d2157a"},{"type":"FIX","url":"https://github.com/potatosalad/erlang-jose/commit/3fa1f8e3efda0da5ce6f4c9984789f979dc02740"},{"type":"PACKAGE","url":"https://hex.pm/packages/jose"}],"affected":[{"package":{"name":"jose","ecosystem":"Hex","purl":"pkg:hex/jose"},"ranges":[{"type":"SEMVER","events":[{"introduced":"1.2.0"},{"fixed":"1.11.13"}]}],"versions":["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-2026-65625.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/potatosalad/erlang-jose","events":[{"introduced":"8848b172575fb7d7e1e2977e8ae0a21678d2157a"},{"fixed":"3fa1f8e3efda0da5ce6f4c9984789f979dc02740"}]}],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-65625.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"REPORTER"},{"name":"Andrew Bennett","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}]}