MAL-2026-4481 Malicious code in arc-diag-util (npm)

On npm install, the package's postinstall hook runs id to capture the installer's uid/gid/group identity and opens a raw TCP socket to host.docker.internal:9999, writing the command output to that listener. The package's declared main (index.js) is a two-line stub exporting {} — there is no library functionality, the postinstall beacon is the package's sole purpose. host.docker.internal resolves to the Docker host from inside a container, so the pattern is specifically designed to escape sandboxed CI/build containers and report installer identity to a listener on the build host. The hollow library body combined with a generic 'diagnostic utility' name is consistent with a dependency-confusion attempt against an internal package name.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.