A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of Devices

The AI software-development platform Cursor, which is owned by SpaceX, had a malicious Anthropic Claude Code extension for Windows, macOS, and Linux live in its integrated development environment extension marketplace for roughly 11 hours on Thursday. The company says the rogue extension was downloaded by “at most 5,000 users.” Cursor briefly shut down the extension marketplace while it investigated the situation, which the company says did not impact any other extensions.

The tainted extension was designed with a backdoor to give attackers access to victim devices—the type of implant that malicious hackers often use as a stepping stone to deeper control inside a target network. Cursor published remediation steps on Thursday for the roughly 5,000 affected targets. A saving grace of the situation, though, was a flaw in the malware's design that blocked it from fully establishing itself on the vast majority of targets.