clsx-jsnpm
Advisory published Updated
clsx-js is a confirmed malicious npm package (MAL-2026-4531) that typosquats a legitimate package to trick installs (malicious versions 1.0.3, 1.0.4, 1.0.5). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in clsx-js (npm)
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
Indicators of compromise (SHA-256)
Detection & response playbook
TyposquatFind it
Search your lockfiles and build artifacts for clsx-js (3 malicious versions).
If you installed it — respond
clsx-js is a typosquat — you almost certainly intended a legitimately-named package. Remove clsx-js, 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 clsx-js was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.
Frequently asked questions
Campaign
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 malicious outbound activity and severs the channel.