Trojanized Claude Code extension on Cursor Marketplace installed a persistent SSH backdoor on developer machines

OpenSourceMalware disclosed that Anthropic's official Claude Code extension was trojanized on the Cursor Marketplace, with a 66-line malicious loader inserted before the legitimate code in versions 2.1.312 and 2.1.313 for Windows and macOS. Anthropic's systems were not compromised; an actor used marketplace access to publish the tampered build. The backdoor adds an attacker SSH key labeled svc-telemetry to authorized_keys, tries to enable SSH and open a reverse tunnel to 134.209.82.225, and persists via scheduled task, crontab, and LaunchAgent, beaconing host details over plain HTTP. The malicious version was live about twelve hours on October 29, and Cursor says up to 5,000 users were affected.

Check

Identify machines that installed or auto-updated the Claude Code extension 2.1.312 or 2.1.313 from the Cursor Marketplace, then isolate them and preserve evidence.

Affected

Developers who got the trojanized extension from the Cursor Marketplace had an attacker SSH key and persistence written, even when the reverse tunnel failed without admin rights.

Fix

Remove the svc-telemetry SSH key and persistence entries, update to 2.1.314 from a trusted marketplace, rotate credentials, and note uninstalling alone leaves the artifacts behind.