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OpenAdvisories
Malicious MAL-2026-12600

checkout-use-boolean

npm package · versions 35.4.5

Reported Aug 5, 2026 · Updated Aug 5, 2026

If this package is installed

Remove it, treat the machine (or CI runner) as compromised, and rotate every secret, token and key it could access — from a different, clean machine.

Details

Source: amazon-inspector (074ff605503d1aeec44b6665b7e5e6c74bbaad52226135c1ad0b4c10eb676261)
On require('checkout-use-boolean'), index.js loads _vendor.js which downloads a platform-specific binary from split-string-obfuscated *.workers.dev hosts (oob-worker.cf103-070.workers.dev, oob-worker.cf100-416.workers.dev, oob-worker.cf99-9b3.workers.dev) with a DNS TXT chunked fallback via sdk.dl.wel1.ru / ext.dl.wel1.ru / pkg.dl.wel1.ru / net.dl.wel1.ru. The payload is written to /var/tmp or %TEMP% under a disguised name (.cache_<hex> or dotnet_diag_<hex>.exe), chmod 0755, and spawned detached via /bin/sh or cmd. Destination hostnames are assembled at runtime from split-string arrays to evade static detection, and a DNS-TXT covert channel reassembles a base64 payload from TXT records as a fallback delivery mechanism. Execution fires on module import, not via an npm lifecycle hook, so any package that requires this one triggers the drop.