arc-diag-utilnpm
Malicious code in arc-diag-util (npm) Remove it immediately and rotate any exposed credentials.
What this malware does
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.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Backdoor / remote accessFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for arc-diag-util (version 1.0.1). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging arc-diag-util across your stack and pipelines.
If you installed it — respond
arc-diag-util establishes remote access, so treat any host that installed it as fully compromised. Isolate the machine, remove the package, rotate all credentials it could reach, and rebuild from a trusted image rather than cleaning in place — a backdoor may have planted additional persistence.
Did it already run?
If arc-diag-util was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks arc-diag-util before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks arc-diag-util-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the C2 callback and severs the channel.