CVE-2026-65632 ECDSA signature length is not validated in jose, allowing signature malleability
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-65632?
CVE-2026-65632 is a medium-severity vulnerability in potatosalad jose, published on 26 Oct 2026.
Official description
The 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.
As 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.
This issue affects jose: from 1.0.0 before 1.11.13.
Weakness: CWE-347
Which versions are affected by CVE-2026-65632?
1 open source package ship an affected version, including jose.
| Package | Affected | Fixed in |
|---|---|---|
jose Hex | From 1.0.0 | 1.11.13 |
How do I fix CVE-2026-65632?
Upgrade jose to 1.11.13 or later.
Is CVE-2026-65632 being exploited?
There is no known exploitation of CVE-2026-65632 in the wild and no public exploit code.
Sources
Also known as AZL-111161, DEBIAN-CVE-2026-65632, EEF-CVE-2026-65632, GHSA-44hw-rpw9-mwg4, GHSA-6g34-xwc5-pgxj, UBUNTU-CVE-2026-65632.