Cursor Urges Credential Resets After Malicious Claude Code Marketplace Update

The code editor Cursor has issued an urgent warning to software creators who downloaded unauthorized extension packages for cursor claude code from its marketplace. Users are advised to perform deep cleanups on their systems and rotate all accessible sessions and credentials using a completely trusted device. Simply uninstalling the problematic software may leave behind persistent components, according to the warnings issued by the platform.

The concerning packages were identified as versions 2.1.312 and 2.1.313 of Anthropic.claude-code designed for Windows and macOS systems. Cursor's security notices indicate these files were available on October 29, 2026, between the early morning hours and mid-afternoon. The company noted that Anthropic did not create these malicious versions and confirmed no other releases or the official software distribution channels were impacted by the incident.

Always clean affected systems and rotate credentials from a trusted device when malicious extensions are found.

Security researchers at Phorion detailed that the malicious payload attempts to inject an attacker-controlled SSH key, activate the remote-login service on the host machine, and set up a reverse tunnel. Persistence is achieved through specific mechanisms including a macOS LaunchAgent and a Windows scheduled task backed by a Startup-folder method. The injected code executes automatically the moment Node loads the extension module, requiring no further interaction from the user.

Cursor collaborated with its hosting provider to shut down the attacking server, removed the unauthorized packages, rotated its own keys, and rebuilt the marketplace environment. However, these platform-side fixes do not automatically remove files or persistence artifacts already left on local developer machines. Security experts recommend reviewing installation history, isolating compromised endpoints, removing unauthorized SSH keys, and evaluating whether the host operating system needs to be entirely rebuilt.

Why it matters

This incident highlights significant software supply chain vulnerabilities that can impact developers and technical organizations globally. Affected users must clean their host environments and rotate development or financial service credentials to prevent unauthorized access, as persistent components may remain active even after standard software removal.