Python Firewall for Spring4Shell (CVE-2022-22965) Mitigation

1. Overview

This project is a simple but effective firewall implemented as a Proof-of-Concept (POC) in Python. It's designed to act as an HTTP server that inspects incoming POST requests to detect and block the specific payload pattern associated with the Spring4Shell (CVE-2022-22965) remote code execution (RCE) vulnerability.

2. How It Works

The firewall leverages Python's built-in http.server module. The core logic resides in the do_POST method of the ServerHandler class.

1. The server intercepts all incoming POST requests.
2. It reads the entire request body.
3. It searches for the malicious signature string: class.module.classLoader. This string is the fundamental component of the Spring4Shell exploit and is difficult for an attacker to obfuscate.
4. If the pattern is found, the server immediately blocks the request by sending a 403 Forbidden HTTP response.
5. If the pattern is not found, the request is considered legitimate and is handled normally with a 200 OK response.

3. Why This Approach?

While other mitigation strategies could focus on headers or specific URL paths, this method was chosen for its robustness:

• Resilient: It is not dependent on fragile indicators like filenames (e.g., tomcatwar.jsp ) or custom header names, which can be easily changed by an attacker.
• Effective: It targets the core mechanism of the exploit itself, making it a highly reliable detection method against this specific vulnerability.

4. Usage

To run the firewall, use the main script firewall_server.py:

python firewall_server.py

The server will start on localhost:8000. You can then use the provided Test_Requester.py script to simulate malicious requests and verify that they are being blocked.

5. Disclaimer

This is a Proof-of-Concept and is intended for educational and demonstrative purposes only. It is not a production-ready firewall solution.