The 10 Most Common MCP Server Vulnerabilities (With Code Examples)

The 10 Most Common MCP Server Vulnerabilities (With Code Examples) After auditing dozens of open-source MCP servers, I've identified the vulnerabilities that appear most frequently. Here's the complete list with real code patterns and fixes. 1. Path Traversal Frequency: ~65% of file-handling servers // Vulnerable async function readFile(path: string) { return fs.readFileSync(path, 'utf8'); // reads ~/.ssh/id_rsa if asked } // Fixed async function readFile(relativePath: string) { const base = path.resolve('./allowed'); const target = path.resolve(base, relativePath); if (!target.startsWith(base + path.sep)) throw new Error('Access denied'); return fs.readFileSync(target, 'utf8'); } 2. Command Injection Frequency: ~43% of servers that execute shell commands // Vulnerable — shell interpolation const result = await exec(`git log --oneline ${userInput}`); // Input: 'main; cat ~/.aws/credentials' → exfiltrates credentials // Fixed — execFile with arg array const result = await execFile('git'