A Supply Chain Attack Put Malicious Anthropic Claude Extensions on Thousands of Devices — SkimNews
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- Cursor hosted a tampered Anthropic Claude Code extension in its marketplace for approximately 11 hours, which was downloaded by at most 5,000 users across Windows, macOS, and Linux.
- Phorion detected the malicious extension on a customer’s Mac, alerting researchers to the supply chain attack that could have given attackers remote access to devices.
- Anthropic confirmed it did not develop or publish the rogue extension, with technical staff stating the versions on official channels remain unaffected and secure.
- Felix Rieseberg stated on X that a malicious actor exploited access to Cursor’s marketplace to publish a modified version of the Claude Code extension without Anthropic’s involvement.
- David Dworken clarified on X that no Anthropic systems or employee laptops were compromised in the incident, emphasizing the breach was limited to Cursor’s platform.
Why it matters: Up to 5,000 developers were exposed to a backdoored AI tool that could grant attackers persistent access to their devices, yet the flawed malware and rapid detection limited harm. The incident shifts accountability to Cursor for marketplace security, not Anthropic, despite the brand’s association with the extension.
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