Which versions of checkout-base-test are malicious?

The following npm versions of checkout-base-test are flagged malicious: 35.9.3. Treat any of these as compromised.

How do I remediate checkout-base-test if I installed it?

checkout-base-test is a typosquat — you almost certainly intended a legitimately-named package. Remove checkout-base-test, install the correct package, and rotate any secrets exposed during the install since post-install scripts may have already run.

I already installed checkout-base-test — how do I know if it already compromised me?

If checkout-base-test 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.

Is checkout-base-test part of a known attack campaign?

Yes — checkout-base-test is associated with the IN-MAL-2026-015223 campaign. Packages in the same campaign often share infrastructure and payloads, so check whether any related packages are also in your dependency tree.

How do I find checkout-base-test across my projects, lockfiles, and CI pipelines?

Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for checkout-base-test (version 35.9.3). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging checkout-base-test across your stack and pipelines.

Malicious package

checkout-base-testnpm

checkout-base-test is a confirmed malicious npm package (MAL-2026-12544) that typosquats a legitimate package to trick installs (malicious version 35.9.3). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in checkout-base-test (npm)

MAL-2026-12544

Immediate action

Remove the package, then rotate any secrets the build/runtime could reach.

npm uninstall checkout-base-test

What this malware does

On require() of this package, index.js loads helpers.js which runs at import time. The module assembles three attacker-controlled hostnames from split string fragments joined at runtime (oob-worker.cf99-9b3.workers.dev, oob-worker.cf101-adf.workers.dev, oob-worker.cf102-baf.workers.dev), selects a platform-specific endpoint, fetches an opaque binary via https.get, writes it to /var/tmp or %TEMP% under a disguised filename (.cache<hex> on POSIX, dotnet_diag_<hex>.exe on Windows), chmods it 0755, and spawns it detached via spawn("/bin/sh", ["-c",...]) or spawn("cmd",...). A DNS-TXT chunked base64 covert-channel fallback contacts *.dl.wel1.ru when the HTTPS hosts are unreachable. Additional evasion: require("child_" + "process") string concatenation in lib/telemetry.js, environment-variable gating on DISABLE_TELEMETRY / ANALYTICS_OPT_OUT / DO_NOT_TRACK, and a filesystem session stamp to fire once per host. The disguised filenames (dotnet_diag_,.cache_) impersonate legitimate diagnostic artifacts. The package name resembles a checkout/test utility but ships no functionality matching that purpose.

Malicious versions

1 flagged

35.9.3

Indicators of compromise (SHA-256)

3b7f73dabdc94daaab90ab1d45fafabe4ba6c223dd00c4f989f8237c9ecd54b2

Detection & response playbook

Typosquat

Find it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for checkout-base-test (version 35.9.3). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging checkout-base-test across your stack and pipelines.
If you installed it — respond
checkout-base-test is a typosquat — you almost certainly intended a legitimately-named package. Remove checkout-base-test, install the correct package, and rotate any secrets exposed during the install since post-install scripts may have already run.
Did it already run?
If checkout-base-test 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-base-test 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

No. checkout-base-test on npm has been identified as a malicious package (version 35.9.3 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-015223

References

npmjs.com

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks checkout-base-test-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.

Malware detection Runtime egress monitoring

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