Malicious Claude Code extension on Cursor planted SSH backdoors

A trojanized version of Anthropic's Claude Code extension was published to the Cursor IDE marketplace and remained available for 11 hours, during which up to 5,000 developers may have installed it. The malware attempted to establish persistent SSH backdoors by injecting attacker-controlled keys and creating reverse tunnels — giving attackers long-term remote access to compromised developer machines. This incident highlights the inherent trust developers place in IDE marketplaces and how that trust can be weaponised through supply chain compromise. Developer workstations are high-value targets because they often hold source code, credentials, and cloud access — making a successful backdoor here potentially catastrophic for downstream systems.