Anthropic Claude Code extension trojanized on Cursor’s marketplace

What happened

• Cursor says a maliciously modified version of Anthropic’s Claude Code extension (Anthropic.claude-code 2.1.312 and 2.1.313, Windows and macOS) was available on its marketplace from about 02:27 to 13:35 PT on 29 Oct. Cursor says the versions “were not developed by Anthropic”. BleepingComputer cites up to about 5,000 exposed developers (not confirmed by Cursor).
• Technique: a JavaScript loader prepended to extension.js ran on load, added an attacker SSH key (“svc-telemetry”), tried to enable SSH and open a reverse tunnel, and set persistence (LaunchAgent / scheduled task). How the package got published under Anthropic’s name is not disclosed.
• Attribution: none. Found by Phorion and OpenSourceMalware.
• Response: extension removed, marketplace taken down, rebuilt and keys rotated; Cursor says no other extensions were tampered with. Cursor warns uninstalling may not be enough and provides check and remediation scripts.

Sources

• https://cursor.com/blog/claude-code-extension-security-notice
• https://www.bleepingcomputer.com/news/security/malicious-claude-code-extension-on-cursor-planted-ssh-backdoors/

This is a brief: a short, sourced summary from our incident tracking. Full advisories add commands to check whether you are affected.