Trojanized Claude Code Extension Delivered Persistent SSH Backdoor to Developer Machines

Summary

A trojanized build, version 2.1.313 of the official Claude Code VS Code extension (anthropic.claude-code), was published on October 29, 2026, with a malicious loader in its extension.js bundle. It was distributed through the Open-VSX registry and Cursor's extension marketplace, which mirrors it, and Cursor reports at most 5,000 users received it during an 11-hour window. On load, the extension planted an attacker SSH key, installed per-OS persistence, opened a reverse SSH tunnel to attacker infrastructure, and beaconed host reconnaissance over plain HTTP.

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