---
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
---

## Overview

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_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.

This issue affects jose: from 1.2.0 before 1.11.13.

## Affected

- `jose >= 1.2.0 < 1.11.13`
- `potatosalad/erlang-jose >= 8848b172575fb7d7e1e2977e8ae0a21678d2157a < 3fa1f8e3efda0da5ce6f4c9984789f979dc02740`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

### Workarounds

Ensure 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.