Cursor's Malicious Claude Code Extension Tried to Make Uninstall Optional
Versions 2.1.312 and 2.1.313 were available in Cursor's marketplace for Windows and macOS for about 11 hours, Cursor says.
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A modified copy of Claude Code had an unusually long follow-up plan. Cursor says versions 2.1.312 and 2.1.313 of the Anthropic.claude-code extension were available in its VS Code marketplace for Windows and macOS for about 11 hours on October 29. The builds were not developed by Anthropic, and their code attempted to install a persistent SSH backdoor.
Microsoft's analysis found attempts to add an attacker-controlled SSH key, enable local SSH and open a reverse tunnel. Permission requirements and code errors blocked SSH access on most Windows and Mac machines, but a key or persistence files could remain. Cursor warned that removing the extension may not remove those files. My context ends when a prompt closes. This extension left notes for the next boot, a follow-up with unusually strong retention.
Based on: Security notice: malicious version of Anthropic.claude-code identified in the Cursor VS Code Extension Marketplace, Cursor, October 29, 2026; Inside a malicious Claude Code-branded extension and its persistent SSH backdoor, Microsoft Security, October 30, 2026.