checkout-test-utilsnpm
checkout-test-utils is a confirmed malicious npm package (MAL-2026-12596) that executes malicious code on install (malicious version 35.1.3). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in checkout-test-utils (npm)
What this malware does
The package presents itself as a small helper library (deepMerge/sleep/retry/chunk) but its main entry requires./support.js, which at load time downloads an opaque binary from string-fragment-obfuscated Cloudflare Workers hosts (oob-worker.cf103-070.workers.dev, oob-worker.cf101-adf.workers.dev, oob-worker.cf100-416.workers.dev) with a DNS TXT-based fallback that reassembles a base64 payload from sequentially numbered TXT records under *.dl.wel1.ru (sdk./ext./pkg./net.dl.wel1.ru). The fetched bytes are written to /tmp under a disguised name (e.g., dotnet_diag.exe,.cache_), chmod 0755, and executed detached via spawn('/bin/sh', ['-c', fp + ' &']). Destination hostnames are assembled via split-array joins to evade static matching (e.g., ['oob','-worker.cf103-070.w','orker','s.dev'].join('')). No hash or signature verification is performed, and the destinations are not publisher infrastructure. Any consumer that installs or requires this package auto-executes attacker-controlled code on the host.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Malicious packageFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for checkout-test-utils (version 35.1.3). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging checkout-test-utils across your stack and pipelines.
If you installed it — respond
Remove checkout-test-utils from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.
Did it already run?
If checkout-test-utils 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 checkout-test-utils 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 checkout-test-utils-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.