Cursor removes malicious Claude Code extension builds

Cursor said malicious Claude Code extension versions 2.1.312 and 2.1.313 were available in its marketplace on Oct. 29, 2026, from about 2:27 a.m. to 1:35 p.m. Pacific, and that those builds were not developed by Anthropic. Cursor said the builds tried to install a persistent SSH backdoor, that the remote-login step would fail on most hosts, and that it removed the builds and briefly shut the marketplace. Ars Technica reported on Oct. 30 that version 2.1.313 went out through Anthropic's official Cursor account, that at most 5,000 users were affected, and that Anthropic had not issued its own notice.