Backdoored Anthropic Extension Stayed Live on Cursor for Nearly 12 Hours

A version of Anthropic's VS Code extension that had been altered to include a backdoor was available to Cursor users for nearly 12 hours. It was distributed through what is described as Anthropic's verified Cursor account, and that detail is what makes the incident stand out. A listing that carries the credibility of an official publisher gives people little reason to question what they are installing.

The reporting so far does not say how the attackers gained access to that account. Phished credentials, a stolen publishing token, or a hijacked session would each point to a different fix, and until the cause is explained, the exposure window is the firmest fact available. Readers should also watch for a fuller account from Anthropic or Cursor that confirms when the malicious build appeared, when it was removed, and how many installs it reached.

For developers, the practical step is straightforward. If you installed or updated the Anthropic extension in Cursor during that period, treat the machine as potentially exposed. Remove the extension, review what it had permission to read and run, and rotate any API keys, tokens, or other credentials that were reachable from your editor environment. Checking installed extension versions against the publisher's official release notes is a reasonable habit to adopt regardless of how this particular incident is resolved.