🚨Malicious Claude Code Extension Hits 5,000 Developers on Cursor Marketplace

Check your Cursor extensions before your next commit

A malicious version of the Claude Code extension, v2.1.313, was published to Cursor's marketplace and downloadable for roughly 11 hours on Thursday. Up to 5,000 developers may have installed it before it was pulled. The catch? Installing the latest version doesn't remove the persistence mechanism, so updating alone won't save you. If you use Cursor with third-party extensions, this one is your problem. The extension collected host machine details, usernames, configured Git emails and public IP addresses, then forwarded them to the attacker. It also dropped the attacker's SSH key on the machine. That gives someone a foothold on your laptop, with access to your repos and credentials, long after you've uninstalled the extension. The backdoor tried to open a reverse SSH tunnel, which needed admin rights on macOS and Windows. Most victims didn't have them, so that part failed. The data exfiltration and key drop still worked. EDR vendor Phorion caught the package, the marketplace was taken offline as a precaution, and the cloud host blocked the attacker's server. Checks found no other compromised extensions. Worth watching: whether the attacker reuses that key on other machines, and whether Cursor adds stronger publisher verification to its marketplace.