“A malicious actor used access to Cursor’s marketplace to publish a tampered copy of the Claude Code extension, which we didn’t build or publish.”
Up to 5,000 developers installed a backdoored copy of an “official” extension. Anthropic says it wasn’t them. Cursor won’t say how the attacker got publish access to its own marketplace. That silence is the story. The only thing that saved most victims was a buggy implant that needed admin rights.