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Ars Technica AI

Anthropic Claude VS Code Extension on Cursor Backdoored for Nearly 12 Hours

A malicious version of Anthropic's official Claude VS Code extension, version 2.1.313, was distributed through Anthropic's official account on the Cursor marketplace and affected at most 5,000 users. The compromise lasted nearly 12 hours before Anthropic pushed version 2.1.314, according to researcher Kevin Beaumont. Security firm Phorian described it as a supply-chain compromise in which attackers gained access to the official distribution channel and sought cloud credentials. Neither Cursor nor Anthropic has explained how the account was taken over, and Anthropic has not warned customers, the report says.

AI Brief

It is a concrete supply-chain security incident affecting AI developer tooling, with direct implications for teams using Cursor and Claude extensions.

An official extension for Anthropic’s Claude model was backdoored and threatened as many as 5,000 developers' machines, multiple sources reported Friday. Anthropic so far has yet to warn customers of the incident.

The compromised package was a VS Code extension available in the marketplace of Cursor, a maker of AI-assisted developer tools, the company said Friday. The malicious version, 2.1.313, subsequently affected “at most 5,000 users,” presumably when they either downloaded it or their systems automatically fetched and installed it. Anthropic pushed version 2.1.314 several hours after the previous version became available on Cursor, according to independent researcher Kevin Beaumont. Both Beaumont and the CTO and co-founder of security firm Phorian said that version 2.1.313 was distributed through Anthropic’s official account on Cursor. So far, neither Cursor nor Anthropic has explained how the attackers gained control of the account.

In search of cloud credentials

“It was a supply-chain compromise where the attacker gained access to the official distribution channel,” Phorian CTO and co-founder Luke Roberts told Ars. “The malicious version 2.1.313 was posted to the official Anthropic account, effectively superseding 2.1.312. Extensions auto-update in Cursor by default, but users can configure this in settings.” Phorian has more details here.

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