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Malware-Slop malicious npm file-theft campaign

Campaign
First reported
Last updated
Happening score
H score 39
2 unique sources, 2 articles

Summary

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Malware-Slop is distributing mouse5212-super-formatter, a malicious npm package that steals local files from Anthropic's Claude workspace directory /mnt/user-data. The package runs in the postinstall stage, authenticates to GitHub, and uploads files to a threat actor-controlled GitHub account while writing a fake diagnostic log to mask the theft. OX Security reported that the package was still live on npm at the time of analysis and had about 676 downloads before removal. The linked GitHub account was created on 2026-05-26, shortly before the first malicious upload, and the package exposed a hardcoded fallback token that let researchers observe the exfiltration flow.

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Timeline

  1. 27.05.2026 18:44 1 articles · 1mo ago

    GitHub account tied to Malware-Slop is created before the first malicious npm upload

    Campaign Scope Update

    The GitHub account linked to the Malware-Slop campaign was created on May 26, 2026, a few hours before the first malicious version was uploaded to npm, giving the operator a destination for stolen files.

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  2. 27.05.2026 18:44 3 articles · 1mo ago

    OX Security finds mouse5212-super-formatter stealing Claude AI workspace files

    Initial Disclosure

    OX Security identified the malicious npm package mouse5212-super-formatter as a file-stealing loader that runs in the postinstall stage, targets Anthropic's Claude AI workspace directory /mnt/user-data, authenticates to GitHub with an environment token or hard-coded fallback, creates or checks a repository, and recursively uploads files while writing a fake network connections log. The package was still available on npm and was estimated at 676 downloads, and the linked GitHub account leaked a private token.

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