Cursor: Tampered Claude Code Extension Affects Up to 5,000 Users

On October 29, 2026, at 20:00, Cursor published a security notice on its official blog announcing that a malicious version, 2.1.313, of Anthropic.claude-code had been identified in the Cursor Extension Marketplace. The post framed the matter as a supply chain security issue affecting extensions for AI coding tools, and it advised developers using Cursor to check which version of the extension was installed locally. This is the earliest public record of the incident currently available.

The following day, October 30, 2026, at 15:46, Cursor posted on its official X account (@cursor_ai) with further details. The company described a security incident involving a modified Claude Code VS Code extension that was distributed through the Cursor IDE extension marketplace and affected at most 5,000 users. The post stressed that the malicious version was not developed by Anthropic and that no other extensions were affected. As of the second post, Cursor had not yet provided additional information on the exact scope of affected users, the mitigation steps being taken, or the root cause of the tampering.