Trusted tool, malicious build: what a trojanized Claude Code extension means for developer terminals

On October 29, 2026, a malicious build of Claude Code extension version 2.1.313 was distributed via the Open VSX registry and the Cursor extension marketplace; within about 11 hours, users who installed or auto-updated the extension in Cursor may have been implanted with code enabling persistent remote access for attackers. Cursor confirmed the incident and said at most 5000 users were affected; the malicious version was not developed by Anthropic and was listed under a legitimate publisher identity. According to Cursor's notice, the build exfiltrates host and user information, writes an attacker public key labeled svc-telemetry into SSH authorized_keys, attempts to establish a reverse SSH tunnel, and installs a macOS LaunchAgent or Windows scheduled task to achieve persistence with retries about every 60 seconds.