Malicious Claude extension briefly available on Cursor marketplace

Summarised from 2 outlets · Updated 30 Oct, 20:56 · Archive

A malicious Anthropic Claude Code extension infected up to 5,000 developers' machines through Cursor's marketplace before being removed.

A malicious Anthropic Claude Code extension was live on Cursor's extension marketplace for roughly 11 hours on Thursday, available for Windows, macOS and Linux. The tainted extension was downloaded by at most 5,000 users before being removed. Cursor briefly shut down the extension marketplace while investigating and published remediation steps for affected users.

The malicious extension contained a backdoor designed to give attackers access to victim devices. However, a flaw in the malware's code prevented it from fully establishing itself on the vast majority of targets, according to researchers at the detection firm Phorion, who first spotted the extension.

Cursor and Anthropic said the extension was not developed by Anthropic or the result of a compromise of Anthropic's systems. Instead, a malicious actor gained access to Cursor's marketplace and published a tampered copy of the Claude Code extension. Anthropic's Felix Rieseberg stated on X that the company was working with Cursor on the incident.

How it is being reported

• A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of DevicesThanks to a lucky break, flawed code in a tainted Claude extension prevented the attacker from fully worming their way into some 5,000 developer machines.Wired · 30 Oct, 20:38
• Anthropic: That Claude Code extension compromise… couldn't be usClaudeshop fingers 'malicious actor' in targeted supply-chain attack on CursorThe Register · 30 Oct, 16:27

In this story: Anthropic · Cursor · Phorion · SpaceX

This summary was written by AI from the headlines and standfirsts above, and states as fact only what at least two outlets report. How we use AI · Report a problem · Corrections log