Trojanized Claude Code Extension Delivered Persistent SSH Backdoor to Developer Machines

On October 29, 2026, trojanized builds (versions 2.1.312 and 2.1.313) of the official Claude Code VS Code extension were published to Cursor's VS Code Extension Marketplace, targeting macOS and Windows users. The malicious extensions delivered a persistent SSH backdoor to developer machines. This represents a supply chain attack targeting developers who use the Claude Code extension within the Cursor IDE environment. The attack leveraged the trusted distribution channel of the VS Code Extension Marketplace to reach a wide audience of developers. The persistence mechanism via SSH backdoor allows attackers ongoing remote access to compromised developer machines, posing significant risks to source code, credentials, and downstream software projects.