Cursor says a tampered version of the Claude Code extension was listed in its VS Code extension marketplace on a Thursday, for about eleven hours. As many as 5,000 users may have been affected. Anthropic had no role in developing the code.
The extension tried to collect the hostname, username, operating system and public IP address of the machines it ran on. It also tried to set up remote access for the attacker, though Cursor believes this would likely have failed on most machines because it requires admin privileges.
After finding the problem, Cursor pulled the extension and took the entire marketplace offline. It was reinstated once providers had neutralized the malware and Cursor had confirmed there was no further risk. Cursor says no other extensions were affected.
Why it matters if you build agents
Developers who installed the Claude Code extension in Cursor recently should check which version they have and remove any build that does not match the official one.
Extensions run with access to the machine they are installed on, so their publisher and requested permissions deserve the same scrutiny as any other dependency.
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