Cybersecurity researchers have identified a malicious version of Anthropic’s Claude Code extension that was distributed through the Cursor Marketplace as a legitimate update. The compromised extension, version 2.1.313, was designed to install a persistent SSH backdoor on affected systems. Cursor temporarily closed its marketplace to remove the malicious package after discovering the incident. According to Cursor, up to 5,000 users downloaded the trojanized extension between approximately 2:27 a.m. and 1:35 p.m. PT on October 29, 2026. The exact method attackers used to introduce the unauthorized update has not been disclosed.
The malicious extension contained code that would activate after VS Code startup and add an attacker-controlled SSH key to users’ systems while attempting to establish a reverse tunnel to an external server. The extension also gathered sensitive system information including IP addresses, usernames, operating system details, and names of environment variables containing credentials. On most macOS and Windows hosts, the extension lacked administrative rights needed to fully enable remote SSH access, though it still added the attacker’s SSH key and established persistence mechanisms. Anthropic has released version 2.1.314 to address the vulnerability, and affected users are advised to isolate their systems and rotate credentials.
Source: Read the full story at The Hacker News
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