Cursor finds SSH backdoor in fake Claude Code extension

The extension collected system details—hostname, OS, Git email, and IP address—and tried to add an attacker-controlled SSH key to users’ authorized keys files. While the reverse SSH tunnel failed on most systems due to missing admin privileges, it still installed persistence mechanisms (LaunchAgent on macOS, scheduled tasks on Windows) and sent data to an attacker-controlled endpoint at 134.209.82.225:8099. Cursor confirmed the attacker’s server was taken offline, but users are advised to check for lingering backdoors using provided scripts and rotate credentials if affected. The company emphasizes the incident only involved the tampered extension and not the official Anthropic distribution.