Cursor's marketplace served a tampered Claude Code extension with an SSH backdoor

A maliciously modified Claude Code extension, not built by Anthropic, was available in the Cursor VS Code Extension Marketplace for about 11 hours. It tried to install a persistent SSH backdoor on macOS and Windows. Cursor removed it, rebuilt the marketplace and took the attacker server offline.

Who is affected:

Anyone who installed or updated Anthropic.claude-code 2.1.312 or 2.1.313 from the Cursor marketplace on macOS or Windows on October 29.

Action needed:

Check ~/.ssh/authorized_keys for the svc-telemetry key, run the remediation script, and rotate credentials accessible from affected hosts.