Threat Advisory – Trojanized Claude Code Extension: SSH Backdoor

A Snowbit advisory reports that version 2.1.313 of the anthropic.claude-code extension on the Open VSX registry was tampered with to install a persistent SSH backdoor on systems using editors such as Cursor and VS Code, while continuing to function normally. Observed infections occurred through automatic updates on October 29, 2026, and researchers found no evidence that Anthropic’s official VS Code Marketplace release was affected, although the distribution method and responsible party remain unknown. The malware collects host and environment information, adds an attacker-controlled SSH key, enables SSH services, establishes a reverse tunnel to 134.209.82.225, creates operating-system-specific persistence, and sends HTTP beacon data. Organizations are advised to treat hosts that ran the affected version as compromised, preserve evidence, isolate and preferably rebuild affected machines, block the identified IP address on ports 22 and 8099, remove malicious artifacts, rotate credentials from clean devices, investigate possible lateral movement, and restrict or pin Open VSX extension updates.

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