MAL-2026-12600 Malicious code in checkout-use-boolean (npm)
Malicious package
Published
MAL-2026-12600 is a malicious package: checkout-use-boolean (npm). Every version was published to cause harm.
Task:
1. Search this repository's dependency manifests and lockfiles for the package, including transitive dependencies.
2. If it is present, remove it, regenerate the lockfile with the project's package manager, and replace whatever it was used for.
3. List any CI runners, developer machines or containers that installed it, so their secrets can be rotated.
4. If the package is not used anywhere, say so and change nothing.
Reference: https://insights.sbomify.com/MAL-2026-12600/ (Markdown: https://insights.sbomify.com/MAL-2026-12600/index.md)
- Package
- checkout-use-boolean
- Registry
- npm
What is MAL-2026-12600?
MAL-2026-12600 is a malicious package in checkout-use-boolean, published on 5 Aug 2026.
Official description
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.
What should I do about MAL-2026-12600?
Remove the package from your dependencies and lockfiles, then rotate any secrets on machines where it was installed.