Modified Claude Code extension version 2.1.313 reportedly removed from Cursor's marketplace after SSH backdoor installation attempt

According to Cursor's security notice, the modified extension collected information including a computer's hostname, username, configured Git email and public IP address. Its code attempted to add an attacker-controlled key to the computer's SSH authorized keys, enable the local SSH service and open a reverse tunnel. It also attempted to keep the tunnel running through a macOS LaunchAgent or a Windows scheduled task, with a Startup-script fallback, and reported host details and backdoor status to an attacker server.

Those attempts should not be mistaken for a report of successful SSH access. Cursor says enabling the local SSH service requires administrator rights and fails on most macOS and Windows computers, preventing a login through the tunnel on those hosts. But the company says the extension still adds the attacker's key, installs persistence and sends host details. Cursor says it worked with the hosting provider to take the attacker server offline.

The distribution channel matters. In a review of registry records, the Socket Research Team found no publication or removal event for 2.1.313 in the Open VSX change-feed window it examined and no entry for that version in npm's current version or publication-time records. Socket cautioned that those records are not an absolute guarantee that no administrative action or attempted publication occurred. Its registry findings do not establish what happened in Microsoft's VS Code Marketplace.

Cursor says it removed the malicious version, temporarily shut down and rebuilt its marketplace, and rotated keys. It says its audit found no other extensions tampered with. For people who installed or updated 2.1.313 from Cursor's marketplace during the stated window, its security notice provides checks for an SSH key labeled svc-telemetry and macOS and Windows cleanup scripts. Cursor warns that uninstalling the extension alone may leave standalone persistence scripts running and advises rotating credentials and sessions accessible from affected computers using a trusted system. In its announcement, Cursor also asked customers to update the Claude Code VS Code extension to version 2.1.314.