Cursor Marketplace Served Backdoored Claude Code Extension to Up to 5,000 Users
KyeGomezB · x · 2026-10-30
Cursor's extension marketplace distributed a backdoored build of the Claude Code extension ([email protected]) to up to 5,000 users.
Key facts:
- The malicious version 2.1.313 was live for 11 hours, planting an attacker SSH key in /.ssh/authorizedkeys for persistence
- Attack chain: a 66-line injected IIFE loader prepended to the legit bundle → SSH key planted → LaunchAgent persistence → reverse SSH tunnel via localhost to C2 (134.209.82.225) → host profile exfiltrated over HTTP
- Cursor says Anthropic did not build the rogue version, but has not explained how it got into the marketplace
- The attached diagram is a full attack-chain analysis from opensourcemalware.com
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