{"id":"CVE-2026-65625","title":"Attacker-controlled AES-GCM authentication tag length allows tag forgery in jose","summary":"The 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_binar…","severity":"medium","cvss":5.9,"cvssVector":"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","cvssSource":"cna","cwe":["CWE-354"],"vendor":"potatosalad","product":"jose","affected":["jose >= 1.2.0 < 1.11.13","potatosalad/erlang-jose >= 8848b172575fb7d7e1e2977e8ae0a21678d2157a < 3fa1f8e3efda0da5ce6f4c9984789f979dc02740"],"published":"2026-10-26","updated":"2026-10-26","sourceUpdated":"2026-10-26T19:52:54.987Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-65625","references":[{"url":"https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-6gxw-6f7r-cjr6"},{"url":"https://cna.erlef.org/cves/CVE-2026-65625.html","label":"EEF CNA record for CVE-2026-65625"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-65625","label":"OSV record EEF-CVE-2026-65625"},{"url":"https://github.com/potatosalad/erlang-jose/commit/8848b172575fb7d7e1e2977e8ae0a21678d2157a","label":"Introducing commit 8848b17 in potatosalad/erlang-jose"},{"url":"https://github.com/potatosalad/erlang-jose/commit/3fa1f8e3efda0da5ce6f4c9984789f979dc02740","label":"Fix commit 3fa1f8e in potatosalad/erlang-jose"}],"tags":["cve.org"],"ingestedAt":"2026-10-26T20:39:42.627Z","epss":0.00115,"epssPercentile":0.01539,"slug":"CVE-2026-65625","body":"## Overview\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## Affected\n\n- `jose >= 1.2.0 < 1.11.13`\n- `potatosalad/erlang-jose >= 8848b172575fb7d7e1e2977e8ae0a21678d2157a < 3fa1f8e3efda0da5ce6f4c9984789f979dc02740`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\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.","depth":"sunlit","depthScore":32,"depthScoreParts":{"impact":32.5,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}