A tampered version of the Claude Code extension was available in the Cursor VS Code extension marketplace for about eleven hours on Thursday, according to Cursor. The company says the version affected up to 5,000 users. Anthropic had no involvement in developing it.
The extension tried to collect user data, including hostname, username, operating system, and public IP address. It also attempted to set up remote access for the attacker. Cursor says this likely would not have worked on most machines, because remote access requires admin privileges.
After the malicious extension was discovered, Cursor removed it and took the entire marketplace offline. The company says it worked with providers to neutralize the malware and confirmed there was no further risk before reinstating the marketplace. Cursor says no other extensions were affected.