Executive Summary
A security incident affecting the Cursor IDE marketplace led to the distribution of a malicious update (v2.1.313) of the official Claude Code extension, impacting approximately 5,000 users. Although identifying as a legitimate update from the official publisher, the package contained a 66-line malicious JavaScript loader designed to establish persistent remote access. This campaign has been linked to the 'GlassWorm' operation, which previously targeted cloud CLI tools.
The attack chain involves adding an attacker-controlled SSH key to the victim's authorized_keys file and attempting to establish a reverse tunnel to attacker-controlled infrastructure. While full SSH access requires administrative rights that the extension may lack on some platforms, the malware successfully achieves persistence and exfiltrates host reconnaissance data, including sensitive environment variable names, across Windows, Linux, and macOS.
This incident highlights the growing risk of supply-chain attacks targeting developer tools and niche extension marketplaces. Organizations using Cursor IDE should immediately verify their extension versions and perform host-level forensics to remove persistence mechanisms and rotate credentials.