
Inside a malicious Claude Code-branded extension and its persistent SSH backdoor
Microsoft Threat Intelligence analyzes a tampered anthropic.claude-code extension (versions 2.1.312 and 2.1.313) served on the Cursor marketplace on 29 October 2026. The injected JavaScript loader adds an SSH key labeled svc-telemetry, opens a reverse SSH tunnel and sets up persistence on macOS, Linux and Windows. The post gives cleanup steps, IOCs and Defender XDR hunting queries. VS Code Marketplace and npm were not affected.
Supply Chain, Blue Team & Detection, Malware & RE· Published and added 31 Oct 2026













