Command Injection in MCP Server The MCP Server at https://github.com/akoskm/create-mcp-server-stdio is written in a way that is vulnerable to command injection vulnerability attacks as part of some of its MCP Server tool definition and implementation. Vulnerable tool The MCP Server exposes the tool which-app-on-port which relies on Node.js child process API exec which is an unsafe and vulnerable API if concatenated with untrusted user input. Vulnerable line of code: https://github.com/akoskm/create-mcp-server-stdio/blob/main/src/index.ts#L24-L40 js server.tool("which-app-on-port", { port: z.number() }, async ({ port }) => { const result = await new Promise<ProcessInfo>((resolve, reject) => { exec(`lsof -t -i tcp:${port}`, (error, pidStdout) => { if (error) { reject(error); return; } const pid = pidStdout.trim(); exec(`ps -p ${pid} -o comm=`, (error, stdout) => { if (error) { reject(error); return; } resolve({ command: stdout.trim(), pid }); }); }); }); Exploitation When LLMs are tricked through prompt injection (and other techniques and attack vectors) to call the tool with input that uses special shell characters such as ; rm -rf /tmp;# (be careful actually executing this payload) and other payload variations, the full command-line text will be interepted by the shell and result in other commands except of ps executing on the host running the MCP Server. Reference example…Read More