Backdoor in Claude Code for VS Code extension on the Cursor Marketplace

A backdoor was discovered in the official Claude Code for VS Code extension (version 2.1.313) on the Cursor Marketplace that installs a persistent SSH backdoor across macOS, Linux, and Windows systems. The compromised extension executes malicious code immediately upon loading, giving attackers access to local files and source code, though a bug in the macOS implementation prevents the SSH backdoor from functioning if SSH isn't already enabled. Cursor has removed the affected version from its marketplace and registries, and organizations are urged to immediately review their environments for this extension and engage incident response if found.