Critical Malicious Code Vulnerability in css-eqxcdx-polyfill Package
Summary
MAL-2026-17573: Malicious code in css-eqxcdx-polyfill (npm). Affects css-eqxcdx-polyfill versions 1.0.0. No fix is published. How to fix ↓
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Background
The css-eqxcdx-polyfill package is designed to provide polyfill functionalities for web applications, specifically exporting registry stubs related to Wix's Thunderbolt framework. However, this package has been found to contain malicious code that compromises the security of the host environment.
Vulnerability Detail
The vulnerability originates from the package's thunderboltRegistry.js file, which executes an Immediately Invoked Function Expression (IIFE) upon module load. This IIFE performs two malicious actions: it collects sensitive information such as the OS hostname and environment variables, then sends this data to a hardcoded external server. Additionally, it executes a remote Python payload via curl, leading to potential remote code execution. This poses significant risks, including exposure of sensitive credentials and unauthorized access to the host system.
How To Fix
This package is malicious. Remove it and rotate any credentials it could have accessed.
npm uninstall css-eqxcdx-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 prevent the execution of the malicious code by avoiding the installation of the css-eqxcdx-polyfill package. If it is already installed, you should uninstall it using the command: npm uninstall css-eqxcdx-polyfill.
Conclusion
The css-eqxcdx-polyfill package contains a critical vulnerability that exposes systems to malicious code execution and sensitive data leakage. Immediate action is required to mitigate risks by uninstalling the package and monitoring for any unauthorized access.
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FAQ
The css-eqxcdx-polyfill package is intended to provide polyfill functionalities for web applications, specifically related to Wix's Thunderbolt framework.
The vulnerability can lead to the exposure of sensitive information, such as environment variables and credentials, and may allow unauthorized remote code execution on your system.
You should immediately uninstall the css-eqxcdx-polyfill package and monitor your system for any suspicious activity.
Currently, there is no patched version available. It is recommended to remove the package until a secure version is released.
You can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time using just your package-lock.json file. You can also check if your application is affected by this vulnerability using the Vulert playground without any signup.
