A tampered Claude Code extension on Cursor’s marketplace planted a persistent SSH backdoor
On October 29, 2026, Cursor’s extension marketplace served a falsified Anthropic.claude-code build (2.1.312 and 2.1.313) for about eleven hours, planting an SSH key and a persistent tunnel on developers’ machines. Up to 5,000 users are affected, and uninstalling the extension is not enough.