An analysis of the compromised official Anthropic Claude Code extension (v2.1.313) distributed via Open VSX and Cursor Marketplace, which injected a malicious loader, added an unauthorized SSH key, and established reverse tunneling.
The issue concerns a malicious version of the Claude Code application, which was made available through the Cursor Marketplace and Open VSX platforms on October 29, 2026. According to the data, the incident affected up to 5.000 users who downloaded the tampered version between 2:27 a.m. and 1:35 p.m. local time.
How the dangerous program worked
The tampered version was numbered 2.1.313 and contained additional code that was added before the regular application code. The program automatically added an access key to the user's computer and attempted to configure the device to be accessible remotely, while also creating a connection to an external address and configuring mechanisms to keep it active.
At the same time, the program collected basic information about the computer, such as the computer name, operating system, processor type, internet address, user folder, Git email, and names of 40 environment variables, sending them to an external address over a simple network.
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Cursor noted that on many Windows and macOS computers, enabling remote access required administrator privileges that the application did not have, causing this part to fail. However, the access key and persistence mechanisms were installed normally.
What the platforms did and what users should do
The issue was identified and the service was temporarily disabled to remove the malware. Anthropic has released the secure version 2.1.314 on both Open VSX and the Microsoft platform until October 30, 2026.
Cursor announced that it will contact affected users directly and recommends that those who used the problematic version isolate their computers, remove any unknown access keys and persistence mechanisms, and change their passwords and login details.
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