Command Injection Vulnerability in MCP File Reader

What is Command Injection Vulnerability in MCP File Reader?

A deliberately vulnerable Python MCP server that demonstrates a critical command injection flaw in its read_file tool, intended for educational security testing.

How to use Command Injection Vulnerability in MCP File Reader?

Install Python 3.12+, MCP library 1.6.0, clone the repository, run mcp install main.py, configure Claude Desktop as shown in the README, then start with mcp dev main.py. Use the MCP Inspector to send malicious file_name values to the read_file tool.

Key features of Command Injection Vulnerability in MCP File Reader

• Uses shell=True in subprocess calls
• Interpolates user input directly into a shell command
• Performs only superficial path validation
• Demonstrates command injection payloads like ; whoami
• Includes a proper fix using shlex.quote() or list arguments

Use cases of Command Injection Vulnerability in MCP File Reader

• Security researchers learning about command injection in MCP servers
• Educators demonstrating the dangers of shell=True with user input
• Practicing exploitation techniques in a safe, local environment

FAQ from Command Injection Vulnerability in MCP File Reader

What is the vulnerability in this server?

The read_file function runs cat {file_name} with shell=True, allowing an attacker to append arbitrary shell commands after a semicolon in the file name.

How can I fix the vulnerability?

Replace the unsafe call with a list argument (subprocess.check_output(['cat', file_name])) or use shlex.quote(file_name) if shell=True is necessary. Also validate that the resolved path stays within the allowed directory.

What dependencies are required?

Python 3.12 or higher and the MCP library version 1.6.0.

Can this server be used in production?

No, this implementation is for educational purposes only and must never be used on production systems or with sensitive data.

How do I connect to the server from an MCP client?

Configure Claude Desktop by editing ~/.config/claude-desktop/claude_desktop_config.json with the appropriate command and arguments as shown in the README.