---
id: CVE-2026-53939
title: >-
  OpenIDC/cjose is a C library implementing the Javascript Object Signing and
  Encryption (JOSE)
summary: >-
  OpenIDC/cjose is a C library implementing the Javascript Object Signing and
  Encryption (JOSE). In versions 0.6.1 through 0.6.2.5, when cjose encrypts a
  JWE using an AES-CBC-HMAC content-encryption algorithm (`A128CBC-HS256`,
  `A192CBC-HS3…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-321
  - CWE-330
vendor: OpenIDC
product: cjose
affected:
  - 'cjose >= 0.6.1, < 0.6.2.6'
published: '2026-09-09'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T19:57:48.533'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-53939'
references:
  - url: >-
      https://github.com/OpenIDC/cjose/commit/2a6e5bd969fa20059fb00913fb9f57d77ea6a4d9
    label: security-advisories@github.com
  - url: 'https://github.com/OpenIDC/cjose/releases/tag/v0.6.2.6'
    label: security-advisories@github.com
  - url: 'https://github.com/OpenIDC/cjose/security/advisories/GHSA-f6wf-pqg3-6wqq'
    label: security-advisories@github.com
  - url: 'https://github.com/OpenIDC/cjose/security/advisories/GHSA-f6wf-pqg3-6wqq'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - cve.org
  - exploit-available
epss: 0.00308
epssPercentile: 0.21079
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-09-09T15:12:10.094529Z'
ingestedAt: '2026-09-09T00:15:28.907Z'
---

## Overview

OpenIDC/cjose is a C library implementing the Javascript Object Signing and Encryption (JOSE). In versions 0.6.1 through 0.6.2.5, when cjose encrypts a JWE using an AES-CBC-HMAC content-encryption algorithm (`A128CBC-HS256`, `A192CBC-HS384`, or `A256CBC-HS512`) together with any key-management algorithm that generates a fresh content-encryption key (CEK), the CEK is all zero bytes instead of being randomly generated. The resulting JWE is therefore encrypted and authenticated under a fixed, publicly known key, so anyone who obtains the JWE can recover the plaintext and forge or modify the content. This is fixed in version 0.6.2.6 by `_cjose_jwe_set_cek_aes_cbc()` generating the CEK from `RAND_bytes`. A regression test asserts that the `encrypted_key` differs across two encryptions for each AES-CBC-HMAC variant. Until upgrading, for data encrypted with cjose, three options are available. Use an AES-GCM `enc` (`A128GCM` / `A192GCM` / `A256GCM`) instead of an AES-CBC-HMAC `enc`,  use `alg=dir` with a caller-supplied CEK, or avoid using cjose for JWE encryption with the affected algorithm pair. These are mitigations for new ciphertexts only; data already encrypted under the zero key remains compromised and should be re-encrypted (and any secrets it contained rotated).

## Remediation

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