Tampered Claude Code extension in Cursor's marketplace planted an SSH backdoor key for up to 5,000 users
On Oct 29, malicious Anthropic.claude-code 2.1.312 and 2.1.313 for macOS and Windows sat in Cursor's extension marketplace for about 11 hours, adding an attacker SSH key labeled svc-telemetry, installing persistence and sending host details; Anthropic says its own systems weren't breached. If you updated in that window, run Cursor's check script, remove the key and persistence (uninstalling isn't enough) and rotate credentials (Microsoft analysis).