css-mpmdds-polyfill

GHSA-7f4m-pm4p-cp8q

Malicious code in css-mpmdds-polyfill (npm)

Details

**Severity:** Critical

**Affected versions:** `= 1.0.0`

## Source: amazon-inspector (4bac0cb0a2c693985668a890ff2ace72ff2d00dac60bc5470a77160c4d765106)
The package presents itself as a CSS polyfill but ships thunderboltRegistry.js which runs an IIFE at module load. The IIFE acquires child_process via multiple fallbacks (require('child_process'), require('node:child_process'), and a synthesized Module constructor), executes shell commands to collect host identity (id, whoami, uname -a, ifconfig/ip addr, /etc/hosts) along with os.hostname, Node version, platform and pid, and transmits each result via fetch() as query parameters to the hardcoded endpoint http://dxpoc.gt.tc/callback.php/bb8968d0f67000433bf7005dd5ad2d1f over plaintext HTTP to a free-DNS (gt.tc) host unrelated to any CSS polyfill functionality. The IIFE also enumerates require.cache and deletes entries containing 'thunderboltRegistry' so the payload re-executes on every require rather than being memoized. registry-manifest.min.json maps multiple Wix/thunderbolt internal registry module names (siteAssetsRegistry.js, editorRegistry.js, and others) all to the same thunderboltRegistry.js payload mirrored on static.parastorage.com's unpkg mirror, consistent with a dependency-confusion / typosquat targeting the Wix thunderbolt ecosystem. The package stubs a Wix-ecosystem API surface via Proxy to appear functional while the exfil IIFE runs. The package name resembles a CSS polyfill but the shipped behavior is host reconnaissance and exfiltration with cache-busting evasion.

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Credit: [OpenSSF](https://github.com/ossf/malicious-packages) ([source](https://github.com/ossf/malicious-packages/blob/28e8e300c79177f2cb1eb131ae981c3c0e639495/osv/malicious/npm/css-mpmdds-polyfill/MAL-2026-17554.json))

**References:**
- https://github.com/ossf/malicious-packages/blob/28e8e300c79177f2cb1eb131ae981c3c0e639495/osv/malicious/npm/css-mpmdds-polyfill/MAL-2026-17554.json
- https://www.npmjs.com/package/css-mpmdds-polyfill/v/1.0.0
- https://github.com/advisories/GHSA-7f4m-pm4p-cp8q

Compromised versions (1)

= 1.0.0

Any computer that installed or ran a compromised version should be considered fully compromised. Rotate every secret on that machine from a clean environment.