Cursor's extension marketplace served malicious Claude Code extension versions 2.1.312 and 2.1.313 for Windows and macOS on October 29
Cursor's security notice, updated October 30, 2026, says maliciously modified versions of Anthropic's Claude Code extension, Anthropic.claude-code 2.1.312 and 2.1.313 for Windows and macOS, were available in the Cursor VS Code Extension Marketplace between about 2:27 AM and 1:35 PM PT on October 29. Cursor says these versions were not developed by Anthropic. Cursor reports host-detail collection and persistence, and describes an attempted SSH backdoor whose key, service and tunnel step would fail outside highly unusual administrator execution. Cursor says uninstalling it may not be enough.