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Malicious package

clsx-jsnpm

Malicious code in clsx-js (npm) Remove it immediately and rotate any exposed credentials.

MAL-2026-4531
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall clsx-js

What this malware does

On npm install, dist/postinstall.js base64-decodes the URL https://api.npoint.io/984b75c022a70cf00c39, fetches JSON from this anonymous mutable JSON-hosting service via axios, and pipes the response's data.content into a detached node child process's stdin for execution. The fetch has no version pin, no hash/signature verification, and the source is operator-mutable — the attacker can swap the executed payload at any time. The package additionally typosquats the widely-used clsx utility (by Luke Edwards): name is a one-token edit, and the description, author name, email, and homepage are copied verbatim from the legitimate clsx to impersonate the upstream maintainer. The genuine clsx ships no postinstall; this fork adds one whose only purpose is the remote-code dropper. A malformed Dependencies (capital-D) field also lists child_process, a known squat name. Installing this package on any machine results in arbitrary attacker-controlled code execution under the installer's user account.

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.

Malicious versions

3 flagged
1.0.31.0.41.0.5

Indicators of compromise (SHA-256)

23e4e85f63d161234d84c774fdff696827934a27282be2ce9ff362a756246ee6
2bc88378968921e5e583cd044040b7ac4c6a516c16741aa082d8e080c18329c0
e280d8130a74a6db6f6960780c8e181e1abfcc2c759d9c31a3d987fa282d27bf
64650ce568f6dcb32276c86bc8e12ed0ea072a19425670e47310e7f4b3b01715

Detection & response playbook

Credential / info stealer
  1. Find it

    Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for clsx-js (3 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging clsx-js across your stack and pipelines.

  2. If you installed it — respond

    clsx-js is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.

  3. Did it already run?

    If clsx-js 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.

  4. How O3 protects you

    O3 blocks clsx-js 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. clsx-js on npm has been identified as a malicious package (versions 1.0.3, 1.0.4, 1.0.5 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-003696IN-MAL-2026-003252IN-MAL-2026-003694GHSA-8jmh-pvvx-wjrf

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks clsx-js-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.

clsx-js (npm) malicious package — MAL-2026-4531 | O3 Security