What changed
A malicious version of the Claude Code extension for Cursor was briefly available in the Cursor VS Code extension marketplace on Thursday, according to the company. The tampered extension attempted to harvest user data, including hostname, username, operating system, and public IP address. It also sought to establish remote access for the attacker, though Cursor noted this would likely require admin privileges to succeed on most machines.
What this means in practice
The compromised extension affected up to 5,000 users, according to Cursor. Once the threat was identified, Cursor pulled the extension from the marketplace and took the entire marketplace offline to prevent further access. After working with providers to neutralize the malware and confirming there was no further risk, the marketplace was reinstated. Cursor stated that no other extensions were affected by the incident.
Limitations and availability
Cursor confirmed that Anthropic had no involvement in the development of the malicious extension. The incident highlights the risks of third-party extensions in software marketplaces. The company emphasized that the malicious version was only available for about eleven hours before being removed. The exact timeline and conditions under which the malicious extension operated are not specified in the announcement.
