CVE-2026-21005 – Docker Registry V2 Schema 1 Image Poisoning

Program Code (Python Flask + Shell)

# docker_registry_sim.py - Simulated registry that serves schema1 manifests
from flask import Flask, request, jsonify

app = Flask(__name__)
images = {
    'myapp': {
        'v1': {'layers': ['sha256:abc', 'sha256:def'], 'config': {}},
    }
}

@app.route('/v2/<name>/manifests/<tag>', methods=['GET', 'PUT'])
def manifest(name, tag):
    if request.method == 'PUT':
        images[name][tag] = request.json
        return jsonify({}), 201
    return jsonify(images[name].get(tag, {}))

if __name__ == '__main__':
    app.run(port=5000)

CVE-2026-21005 – Docker Registry V2 Schema 1 Image Poisoning

Overview

A private Docker registry accepts push requests without authentication and uses Schema 1 manifests, which do not include a content‑addressable configuration digest. An attacker can overwrite an existing tag with a malicious image, and clients pulling that tag will run the attacker’s code.

Vulnerability Details

• Type: Insecure Registry / Supply Chain Attack
• Impact: Container compromise, lateral movement.
• Root Cause: The registry allows unauthenticated pushes and Schema 1 manifests enable tag mutability without integrity verification.

Exploit Demonstration

1. Start the simulated registry:
   root@kitploit:~

   pip install flask
   python docker_registry_sim.py
   

2. Push a poisoned manifest:
   root@kitploit:~

   bash exploit_registry_poison.sh
   

The tag latest is overwritten.