mjs-eslint-helpernpm
Advisory published Updated
mjs-eslint-helper is a confirmed malicious npm package (MAL-2026-6190) that typosquats a legitimate package to trick installs (malicious version 4.0.1). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in mjs-eslint-helper (npm)
What this malware does
The package decodes base64 string literals via Buffer.from(..., 'base64').toString() and pipes the resulting content into execSync('bash...') and execSync('zsh...') invocations in index.js (lines 9, 101, 117, 194, 195). This is the canonical fingerprint of an install-time/import-time dropper: an obfuscated payload is decoded and executed through a shell interpreter, giving the publisher arbitrary code execution on any machine that installs or requires this package. The package name impersonates the eslint helper namespace, consistent with a typosquat lure delivering an active payload. No legitimate eslint helper requires shelling out to bash/zsh from a base64-decoded blob.
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 mjs-eslint-helper (version 4.0.1).
If you installed it — respond
mjs-eslint-helper is a typosquat — you almost certainly intended a legitimately-named package. Remove mjs-eslint-helper, 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 mjs-eslint-helper 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 mjs-eslint-helper-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.