A fake version of the Claude Code extension on the Cursor marketplace installed backdoors

A tampered version (2.1.313) of the official extension for Claude Code, Anthropic's coding assistant, was distributed as a legitimate update on the extension marketplace of the Cursor editor, according to The Hacker News. It was available on October 29 between 2:27 and 13:35, Pacific time, and used the identifier and publisher identity of the legitimate extension. It was discovered by researchers at OpenSourceMalware.

According to that outlet, the malicious code added an SSH key belonging to the attacker to the machine, tried to enable SSH, opened a reverse tunnel to an external server, installed itself persistently and sent data from the machine, such as the public IP, the username, the Git email and the names of environment variables containing keys or tokens.

Cursor said the incident affected at most 5,000 users, that the malicious version "was not developed by Anthropic" and that it will contact those affected directly, according to The Hacker News. Cursor temporarily shut down its marketplace to remove the package, and Anthropic released version 2.1.314. There is no evidence that the tampered version reached Open VSX or the Visual Studio Code marketplace. Users are advised to isolate affected machines, delete the "svc-telemetry" key, remove the persistence, change credentials and update.

Story under review: all the information comes from a single specialist outlet; we have not been able to open Cursor's statement or a statement from Anthropic. It is not known how the fake update was introduced into the marketplace.