The profullstack/mcp-server package contains a critical OS Command Injection vulnerability in its domain_lookup module. The vulnerability arises because user input is concatenated directly into a shell command string without sanitization or escaping and then executed via execAsync(). The affected endpoints POST /domain-lookup/check and POST /domain-lookup/bulk are exposed without authentication and bind to 0.0.0.0, allowing unauthenticated remote attackers to execute arbitrary OS commands as the server process. Proof-of-concept exploits demonstrate successful command execution despite error responses. The CVSS 3.1 score is 9.8 (Critical).