A compromised Claude Code extension was offered through Cursor's VS Code extension marketplace for about eleven hours on Thursday. The incident may have affected up to 5,000 users, according to Cursor. Anthropic had no involvement in developing the extension.
What the extension attempted
The extension tried to collect information about users and their machines, including hostname, username, operating system, and public IP address. These details can identify a device or help distinguish one user environment from another.
It also attempted to establish remote access for the attacker. Cursor said that effort likely would not have worked on most machines because it required admin privileges. The source does not say how many devices, if any, were successfully accessed or whether data was successfully taken.
How Cursor responded
After discovering the tampered extension, Cursor removed it from the marketplace and took the entire marketplace offline. This meant the response extended beyond the single extension while the company and its providers worked to neutralize the malware.
Cursor later said it had confirmed there was no further risk and reinstated the marketplace. It also said no other extensions were affected. The temporary shutdown and subsequent restoration mark the steps described in the company's account of the incident.
What users should take from the incident
The reported exposure was potential, not a confirmed count of compromised devices. Up to 5,000 users may have been affected by the extension's availability, but the report does not establish that every one installed it or that the attempted collection succeeded.
The extension's stated targets—device identifiers and network information—show why software add-ons deserve scrutiny even when they appear in an editor's marketplace. Availability in a marketplace did not mean this tampered version had been developed by Anthropic: Cursor said Anthropic was not involved.
Remote access was another part of the attempted activity, but Cursor's qualification matters. The effort likely would not have worked on most machines because admin privileges were needed. That reduces the scope of what the report claims, without changing the fact that the extension attempted both data collection and remote access.
A limited account of the impact
Cursor's statements provide a clear sequence: the extension appeared for about eleven hours on Thursday, the company pulled it and took the marketplace offline, and the marketplace returned after work with providers to neutralize the malware and confirmation of no further risk.
The account also draws a boundary around the incident: Cursor said no other extensions were affected. It does not provide details about individual users, successful data theft, or confirmed remote access. Those distinctions help readers understand what was reported while avoiding conclusions beyond the available information.