Official Claude Code Extension on Cursor Marketplace Trojanized with Persistent SSH Backdoor

A security incident has emerged involving a trojanized version of the official Claude Code extension hosted on the Cursor Marketplace. According to reporting from BleepingComputer, this specific extension was designed to compromise systems by planting persistent SSH backdoors. The attack targets users of the Cursor editor who installed the extension, allowing unauthorized access to the affected machines through the established SSH bridge. The breach highlights a critical vulnerability in the trust model of third-party extension marketplaces used by developers. Coverage from BleepingComputer emphasizes the technical nature of the threat, specifically focusing on the deployment of the SSH backdoor.

The reports detail how the malicious code was embedded within a tool that users believed to be an official Claude Code extension. By masquerading as a legitimate productivity tool for AI-driven coding, the attackers were able to distribute the malware to a target audience of developers. The outlet notes that the persistence of the backdoor is a primary concern for system security and integrity. To understand why this event is significant, it is necessary to note that the Cursor Marketplace serves as a hub for integrating AI capabilities into the development workflow. When an extension is perceived as official, developers typically grant it significant permissions to interact with their local file systems and environments.

The use of an SSH backdoor is particularly dangerous because it provides a gateway for remote command execution, potentially bypassing traditional security perimeters and allowing attackers to maintain long-term access to sensitive source code and credentials. Future developments will likely focus on the removal of the trojanized extension from the Cursor Marketplace and the identification of all affected users. Based on the facts provided by BleepingComputer, the priority remains for users to check for unauthorized SSH keys or unexpected network connections. While coverage does not yet specify the total number of installations or the specific group behind the attack, the industry will be watching for updates regarding the verification process for extensions to prevent similar supply chain compromises in the future.