GoKawiilFake Claude Code extension on Cursor marketplace installed SSH backdoors
A tampered version of Anthropic's Claude Code VS Code extension, labeled version 2.1.313, was available on Cursor's extension marketplace for about 11 hours on October 29, reaching as many as 5,000 developers. Security researchers at Phorion and OpenSourceMalware found the attackers inserted malicious JavaScript into the extension's main file that ran automatically on load, without any user interaction with Claude Code.
GoKawiil's interpretation of the reporting above, not reported fact.
The incident shows how trusted developer-tool marketplaces can be used to distribute supply-chain attacks that compromise machines at scale, since developers often grant extensions broad system access. Cursor says Anthropic did not create the malicious package but has not explained how attackers managed to publish it under Anthropic's name, leaving open questions about the marketplace's vetting process.
- A malicious Claude Code extension was live on Cursor's marketplace for roughly 11 hours, potentially affecting up to 5,000 developers.
- The malware installed persistent SSH backdoors via LaunchAgents or scheduled tasks and exfiltrated system data to an attacker-controlled IP.
- Cursor confirms Anthropic did not build the fake extension but has not detailed how it was distributed under Anthropic's name.
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Published there as: “Malicious Claude Code extension on Cursor planted SSH backdoors”
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