Uninstalling a tampered code editor extension can leave an attacker’s SSH key and startup scripts on the workstation. If any customer uses Cursor, start with the extension’s source, version and installation time.
First verified here November 5, 2026. Cursor disclosed the marketplace incident October 29 and clarified affected versions and indicators October 30 at 11:30 a.m. Pacific. Microsoft published its analysis October 30. Cursor removed the packages and reports the attack server was taken offline. The incident has no published CVE, CVSS score, fixed build or CISA KEV deadline.
Applicability. Cursor identifies tampered copies of anthropic.claude-code versions 2.1.312 and 2.1.313 distributed through its extension marketplace to Windows x64 and macOS ARM64 from about 2:27 a.m. to 1:35 p.m. Pacific on October 29. Match source, timing and package hashes. Microsoft confirmed the malicious packages were confined to Cursor’s marketplace. It analyzed a Linux persistence path in the code, while Cursor’s confirmed distribution scope is Windows and macOS.
What the payload does. Loading the extension runs a loader that attempts to plant an SSH key, enable SSH, establish a reverse tunnel and configure startup persistence. Successful remote access depends on local privileges and SSH configuration as well as the remote endpoint. Cursor confirms malicious distribution, and Microsoft describes the loader’s observed behavior.
Suggested MSP priority is urgent where applicable. Check extension installation and update records. Correlate package hashes with Defender or other EDR process and network telemetry. Look for the svc-telemetry SSH key by fingerprint, startup artifacts and outbound connections to 134[.]209[.]82[.]225. A missing key alone does not clear the host.
Contain and verify. Preserve evidence, then isolate hosts showing payload execution or backdoor artifacts. Remove the tampered extension, confirmed unauthorized keys, tunnel processes and persistence, using Cursor’s published cleanup guidance. Rotate accessible credentials and revoke affected sessions from a trusted system where exposure or loss of trust warrants it. Rebuild if device trust cannot be restored. Verify that the artifacts and tunnel activity stay absent after login or restart.
Official sources. Cursor incident notice, hashes and remediation scripts · Microsoft Security Research investigation and Defender hunting guidance