A malicious version of Anthropic’s Claude Code extension was live on Cursor’s marketplace for approximately 11 hours. The compromised extension attempted to steal data like hostnames and public IPs and tried to install a persistent SSH backdoor to provide remote access to attackers. Cursor took its entire marketplace offline for several hours to neutralize the threat.
The attack was a supply-chain compromise where attackers accessed Anthropic’s verified Cursor account. The backdoor was designed to work on Windows, macOS, and Linux operating systems. Cursor stated that no other extensions were affected by the incident. Anthropic has not yet issued a public notice to customers about the security incident.
