Anthropic’s VS Code Extension on Cursor Was Backdoored for Nearly 12 Hours

What happened

A backdoored version of Anthropic’s official Claude VS Code extension on Cursor affected at most 5,000 users, according to Cursor. Researchers said malicious version 2.1.313 was distributed through Anthropic’s official account, and Kevin Beaumont reported that Anthropic pushed version 2.1.314 several hours later. Neither company has explained how attackers gained account access, and Anthropic had yet to warn customers.

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Reported by 3 sources

The story so far

Cursor removed a backdoored Claude Code VS Code extension from its IDE marketplace after an incident affecting at most 5,000 users, the company said. The Decoder reported that Cursor temporarily shut down the marketplace and restored it after working with providers to neutralize the malware and confirming there was no further risk. The extension was available for about eleven hours and attempted to collect machine and user information and establish remote access, The Decoder reported. Cursor said the remote-access attempt likely required administrator privileges unavailable on most machines and that no other extensions were affected. Researchers cited by Ars Technica said malicious version 2.1.313 was distributed through Anthropic’s official account. Cursor said Anthropic did not develop the malicious version; that statement concerns who created it, while the researchers’ finding concerns the account used to distribute it. Independent researcher Kevin Beaumont said Anthropic pushed version 2.1.314 several hours later.