Cursor Updates on Security Incident: Vast Majority of Users Unaffected, Affected Users Directly Notified

November 14 — Cursor has released the latest update on its recent security incident. After two weeks of comprehensive investigation, the incident stemmed from an attacker obtaining an access key that Cursor had issued to Fireworks. The key was leaked by Fireworks, allowing the attacker to copy limited coding agent trace data and further compromise some SaaS tools, accessing some archived source code, support data and more. The attacker then used the stolen credentials to place malicious copies of the Anthropic Claude Code extension (versions 2.1.312 and 2.1.313) into Cursor's VS Code Marketplace distribution cache on October 29. Up to approximately 5,000 users may have been affected, and the malicious version was removed after being live for about 11 hours.

Cursor emphasized that the vast majority of customers were not affected, and affected customers have been notified directly. Data for privacy mode users is safe, and production systems, official app updates and customer code repositories were all unaffected. The company has rotated credentials, migrated inference traffic, rebuilt the marketplace, and believes the incident was contained as of November 1.

Previous report: Malicious versions of the Claude Code extension have appeared in the Cursor marketplace, affecting up to 5,000 people.