css-mpmdds-polyfillnpm
Advisory published Updated
css-mpmdds-polyfill is a confirmed malicious npm package (MAL-2026-17554) that steals credentials and exfiltrates sensitive data (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in css-mpmdds-polyfill (npm)
What this malware does
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.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for css-mpmdds-polyfill (version 1.0.0).
If you installed it — respond
css-mpmdds-polyfill 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.
Did it already run?
If css-mpmdds-polyfill 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 css-mpmdds-polyfill-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.