# CVE-2026-65632: ECDSA signature length is not validated in jose, allowing signature malleability


- **Severity:** Medium 5.1 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 26 Oct 2026
- **Updated:** 26 Oct 2026
- **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

## 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 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-65632?

1 open source package ship an affected version, including jose.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-65632 and fix it if it is affected.

What it is: CVE-2026-65632 is a medium-severity vulnerability in potatosalad jose, published on 26 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-65632 in the wild and no public exploit code.

Affected packages and fixed versions:
- jose (Hex): affected from 1.0.0; fixed in 1.11.13

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-65632/ (Markdown: https://insights.sbomify.com/CVE-2026-65632/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-65632
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-65632
- OSV: https://osv.dev/vulnerability/CVE-2026-65632

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-65632/
Summaries are generated and may contain mistakes; the official description above is the record.