Trojanized Claude Code extension on Cursor plants SSH backdoors

· Cybersecurity

A malicious version of Anthropic's official Claude Code extension was distributed through the Cursor Marketplace as a legitimate update, version 2.1.313, for roughly 11 hours on October 29, exposing up to 5,000 developers. Researchers said the package attempted to install persistent SSH backdoors on affected systems. The incident was one of two serious security issues reported against Cursor on the same day, drawing attention to the risk profile of AI-powered integrated development environments, where extensions run with broad access to code and credentials. Developers who installed the update are advised to check their machines for unauthorized remote access.

Why it matters：AI coding assistants and their marketplaces are becoming a high-value supply-chain target, so extension signing and review controls will face new pressure across the developer-tool ecosystem.

Key points

  • The trojanized update circulated for about 11 hours on October 29
  • Up to 5,000 developers may have been exposed
  • It was one of two serious Cursor security issues reported the same day

Sources (original reporting)

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