CVE-2026-65632

What it is

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.

At a glance

Exploitability

Can be exploited locally on the machine without logging in. Limited direct impact.

Exploit odds

0.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-10-26 20:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-11-02 22:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.1% in the next 30 days (EPSS).
• Severity: 5.1 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-10-26 20:17 UTC

Last modified

2026-11-02 22:17 UTC

Exploit probability

0.1% · EPSS, next 30 days

Weakness

CWE-347

Record status

Deferred

Attack profile CVSS 4.0 · 5.1

Attack vector

Local

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-65632.md and follow it. Check whether this project is affected by CVE-2026-65632. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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