Vendor incident, severity critical
Cursor marketplace served malicious Claude Code extension 2.1.313 with persistent SSH backdoor
Published , updated
A tampered Claude Code extension, version 2.1.313, was available in Cursor's VS Code extension marketplace for about 11 hours on October 29, 2026. It added an attacker SSH key to the user's authorized keys, opened a reverse SSH tunnel, set up persistence and sent host details plus the names of credential-like environment variables to the attacker. Cursor says up to 5,000 users were affected, and uninstalling the extension does not remove the backdoor.
What's affected
- cursorevery version
What to do
- Check whether anyone installed or updated to Claude Code extension version 2.1.313 in Cursor or another VS Code-compatible editor.
- Check the SSH authorized keys file for an entry labelled svc-telemetry and run the vendor's cleanup scripts, since uninstalling the extension is not enough.
- Isolate affected machines and consider rebuilding them.
- Using a trusted system, rotate any credentials and sessions the affected machine could reach.
- Check SSH logs for logins from localhost that used the svc-telemetry key.
Secrets to rotate if you were affected
SSH keys, Environment variables, Cloud credentials.
Check whether you were affected
Pharon tells teams automatically when this affects something they run. To check a machine, run this in Claude Code with the Pharon plugin, in the repository that uses it:
/pharon:check-incident cursor-claude-code-extension-backdoor-2026-10References
Notice cursor-claude-code-extension-backdoor-2026-10, signed with key feed-prod-2026-10 (Ed25519). The Pharon CLI verifies the signature before using a notice.