Overview
- Cursor discovered a tampered Claude Code VS Code extension in its marketplace and removed the affected package before briefly taking the marketplace offline for remediation.
- The company says the malicious package tried to install a backdoor, collected basic system data such as IP addresses, usernames and operating systems, and added an attacker-controlled SSH key that could permit remote login.
- Third-party analysts reported the payload ran on load even without user interaction, increasing exposure for users who merely installed or loaded the extension.
- Cursor told users up to 5,000 people may have been affected, is contacting those users directly, rotated security keys, blocked the attacker's server, worked with providers to neutralize the malware, and asked all customers to update Claude Code.
- The episode highlights extension-marketplace supply-chain risk for developer tools and raises the need for tighter vetting, rapid detection and platform controls to protect developer machines and downstream systems.