TL;DR

what: An attacker used access to Cursor's marketplace to publish a trojanized Claude Code extension under Anthropic's legitimate ID, anthropic.claude-code.

impact: Up to 5,000 users installed it between about 2:27 a.m. and 1:35 p.m. PT on October 29, 2026, exposing their hosts to an unauthorized SSH key, persistence and host reconnaissance.

fix: Cursor removed the package, rotated its keys, rebuilt the marketplace, had the attacker's server taken offline and is contacting affected users directly, while its advisory calls for host isolation, removal of the key and persistence, and credential and session rotation.

who: Cursor users who installed anthropic.claude-code versions 2.1.312 or 2.1.313 from the Cursor Marketplace during the window are at risk; no evidence shows the update reached Open VSX or the Microsoft VS Code Marketplace.

Up to 5,000 developers installed a tampered Claude Code extension from Cursor's marketplace on October 29, 2026.…