Malicious npm Package Targets Claude AI Users via Supply Chain Attack

Dev.to / 5/30/2026

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Key Points

  • A malicious npm package, "mouse5212-super-formatter," was found stealing files from Anthropic Claude AI users’ local directories by sending data to a threat actor-controlled GitHub repository.
  • The package masqueraded as a legitimate archive utility and exfiltrated workspace files during the npm postinstall step.
  • The attacker’s weak operational security, including a leaked GitHub token, suggests the malware may be AI-generated or at least produced with limited human expertise.
  • The incident highlights an increasing trend of low-skill threat actors using AI tools to scale supply-chain attacks against popular developer ecosystems.

Forensic Summary

A malicious npm package named 'mouse5212-super-formatter' was discovered exfiltrating files from Anthropic's Claude AI user directory by authenticating to a threat actor-controlled GitHub repository. The package disguised itself as a legitimate archive utility while silently uploading all local workspace files during the postinstall phase. Notably, the attacker's poor operational security — including a leaked GitHub token — suggests AI-generated malware with minimal human oversight, pointing to a growing trend of low-skill threat actors leveraging AI to produce supply chain malware.

Read the full technical deep-dive on Grid the Grey: https://gridthegrey.com/posts/malicious-npm-package-targets-claude-ai-users-via-supply-chain-attack/