A modified version of the Claude Code extension was available in Cursor’s marketplace for about 11 hours, potentially reaching up to 5,000 users, according to reports published October 29 and 30. Its malicious versions tried to plant an SSH backdoor.

Anthropic says its own systems and staff laptops were not compromised and that it did not build the malicious version. A security firm that studied the attack says the extension was distributed through Anthropic’s official Cursor account, which contradicts Anthropic’s account.

Neither Anthropic nor Cursor has said how the attacker got access.

Sources

Image: Laptop Programmcode.jpg by Negative Space, CC0, via Wikimedia Commons. Illustrative photo; it does not show the events described.