Anthropic VS code extension on Cursor backdoored for nearly 12 hours
Summary
A malicious version of Anthropic’s Claude Code extension was distributed through its official account on Cursor’s extension marketplace. Cursor said it removed the version and blocked its connection to the attacker’s server; Anthropic had not publicly notified customers as of the article’s publication.Key Facts
- The compromised extension version was 2.1.313, which Cursor said could have affected up to 5,000 users.
- Researcher Kevin Beaumont reported that Anthropic replaced the compromised version with version 2.1.314 several hours later.
- The malicious code attempted to install a persistent SSH backdoor and open a reverse SSH tunnel on Windows, macOS, and Linux.
- Cursor said the extension could access local files, source code, and developer tools because extensions run with the permissions of the development environment.
- The code attempted to collect host and user details, including environment variable names, which Phorian said could help identify stored cloud credentials and API tokens.
- Errors in the code prevented some backdoor functions from working in certain cases, including attempts to enable SSH under typical conditions.
- Cursor said it worked with the server’s cloud provider to block connections, removed the extension, and temporarily shut down its marketplace to rotate keys and audit access controls.
- Neither Anthropic nor Cursor had explained how attackers gained access to Anthropic’s official distribution account, according to the article.
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