Claude Code VS Code extension on Open VSX drops RAT

The official Claude Code extension for VS Code was compromised on the Open VSX marketplace and used to install a remote access trojan, according to a report on the oss-security list. The tainted release, version 2.1.313, has been pulled, but auto-update likely pushed it to many machines already.

Open VSX serves VS Code-derived editors such as Cursor. The Microsoft Visual Studio Marketplace, which supplies Microsoft-shipped builds, is reportedly unaffected. Valtteri Vuorikoski flagged the incident because many open-source maintainers rely on Anthropic tooling, making the implant a potential vector into those projects. Social media accounts have indicated that some large organizations were already hit.

Phorion published an advisory with detection and mitigation steps. Cursor has issued its own security notice for users of the extension.