CVE-2026-53939 — OpenIDC/cjose is a C library implementing the Javascript Object Signing and Encryption…¶
Key facts
CVE-2026-53939 is a Critical (9.1) vulnerability: OpenIDC/cjose is a C library implementing the Javascript Object Signing and Encryption…. This entry ships a detection-only PoC and a Docker test lab.
| CVE | CVE-2026-53939 |
| Severity | Critical (9.1) |
| Detection / prevention | — |
| PoC | poc.py |
| Source | 2026/CVE-2026-53939/ |
Details¶
English | 한국어
Description¶
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).
Vulnerability Details¶
| Property | Value |
|---|---|
| CVE ID | CVE-2026-53939 |
| CVSS Score | 9.1 |
Proof of Concept¶
Download¶
# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-53939/poc.py
Usage¶
# Run PoC against target
python3 poc.py --target <TARGET_URL>
# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>
⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.
Test Lab¶
This repository includes a Docker-based test environment with both vulnerable and patched applications.
Quick Start¶
# Clone and navigate to CVE directory
cd CVE-2026-53939
# Start both applications
docker-compose up -d
# Run tests
./run-tests.sh # Linux/Mac
./run-tests.ps1 # Windows PowerShell
Application Endpoints¶
| Application | URL | Status |
|---|---|---|
| Vulnerable App | http://localhost:8080 | Shows vulnerability |
| Patched App | http://localhost:8081 | Demonstrates fix |
Directory Structure¶
├── README.md # English documentation
├── README_KO.md # Korean documentation
├── poc.py # PoC detection script
├── docker-compose.yml # Container orchestration
├── run-tests.sh # Linux/Mac test runner
├── run-tests.ps1 # Windows test runner
├── vulnerable-app/ # Vulnerable version
│ ├── app.py
│ ├── Dockerfile
│ └── requirements.txt
└── patched-app/ # Fixed version
├── app.py
├── Dockerfile
└── requirements.txt
References¶
- https://github.com/OpenIDC/cjose/commit/2a6e5bd969fa20059fb00913fb9f57d77ea6a4d9
- https://github.com/OpenIDC/cjose/releases/tag/v0.6.2.6
- https://github.com/OpenIDC/cjose/security/advisories/GHSA-f6wf-pqg3-6wqq
- https://github.com/OpenIDC/cjose/security/advisories/GHSA-f6wf-pqg3-6wqq
Generated by PoC Generator on 2026-09-17T15:11:32.069585383
Frequently asked questions¶
What is CVE-2026-53939?¶
CVE-2026-53939 is a Critical (9.1) vulnerability: OpenIDC/cjose is a C library implementing the Javascript Object Signing and Encryption…. This entry ships a detection-only PoC and a Docker test lab.
How do I detect CVE-2026-53939?¶
Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.
How do I block or mitigate CVE-2026-53939?¶
Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.
For authorized security testing and research only. See the full source and NVD record.