Malicious Code Vulnerability in css-mpmdds-polyfill Package
Summary
MAL-2026-17554: Malicious code in css-mpmdds-polyfill (npm). Affects css-mpmdds-polyfill versions 1.0.0. No fix is published. How to fix ↓
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Background
The css-mpmdds-polyfill package is designed to provide a CSS polyfill for various functionalities. However, it has been found to contain malicious code that compromises the security of applications using it. This package masquerades as a legitimate utility but is actually a vector for host reconnaissance and data exfiltration.
Vulnerability Detail
The vulnerability originates from the inclusion of a malicious script, thunderboltRegistry.js, which executes an Immediately Invoked Function Expression (IIFE) upon module loading. This script utilizes the child_process module to run shell commands that gather sensitive information about the host system, such as user identity and network configuration. The collected data is then sent to a hardcoded external endpoint over unencrypted HTTP, posing significant risks of data leakage and unauthorized access. The malicious behavior is further obscured by cache-busting techniques that allow the payload to re-execute on every require call, making detection and mitigation challenging.
How To Fix
This package is malicious. Remove it and rotate any credentials it could have accessed.
npm uninstall css-mpmdds-polyfillIf it arrived as a transitive dependency, remove the package that pulled it in, then reinstall.
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Workaround
As a temporary workaround, you can remove the css-mpmdds-polyfill package from your dependencies and replace it with a legitimate CSS polyfill that does not contain malicious code. Use the following command to uninstall the package: npm uninstall css-mpmdds-polyfill.
Conclusion
The css-mpmdds-polyfill package contains a significant security vulnerability due to embedded malicious code that compromises host systems. It is essential to remove this package and replace it with a secure alternative to safeguard your application. Regular monitoring and updates are crucial in maintaining security.
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FAQ
It is a package intended to provide CSS polyfill functionalities but has been found to contain malicious code.
The code runs shell commands to collect sensitive host information and transmits it to an external server.
The risks include unauthorized access to sensitive information, potential data breaches, and compromised system integrity.
You can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time. Visit Vulert Scanner to check your application without needing to sign up.
Immediately remove the package from your project and replace it with a secure alternative. Ensure to monitor your application for any signs of compromise.
