Malicious Code Vulnerability in css-reading-flow-polyfill Package
Summary
MAL-2026-17483: Malicious code in css-reading-flow-polyfill (npm). Affects css-reading-flow-polyfill versions 1.0.0. No fix is published. How to fix ↓
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Background
The css-reading-flow-polyfill package is an npm module designed to provide a polyfill for CSS reading flow functionality. However, it has been discovered that this package contains malicious code that compromises the security of applications using it. The package masquerades as a legitimate utility while embedding harmful scripts that can execute unauthorized commands and exfiltrate sensitive information.
Vulnerability Detail
The vulnerability originates from the malicious code embedded in the css-reading-flow-polyfill package, specifically in the thunderboltRegistry.js file. This file impersonates internal Wix thunderbolt registry modules and executes a series of commands using child_process.execSync to gather system information, including user identity and network configuration. It then sends this information to an external server over plain HTTP, posing significant risks of data leakage and unauthorized access. The module also manipulates the require.cache to ensure that the malicious code runs on every require, making it difficult to detect and mitigate.
How To Fix
This package is malicious. Remove it and rotate any credentials it could have accessed.
npm uninstall css-reading-flow-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 avoid using the css-reading-flow-polyfill package altogether and look for alternative libraries that provide similar functionality without the associated risks.
Conclusion
The css-reading-flow-polyfill package contains a serious vulnerability due to embedded malicious code that can compromise system security. It is crucial to remove this package from your project and monitor for any updates or patches. Utilizing tools like Vulert can help keep your applications secure by alerting you to potential vulnerabilities.
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FAQ
It is an npm package intended to provide a polyfill for CSS reading flow functionality, but it has been found to contain malicious code.
The malicious code executes system commands to gather sensitive information and sends it to an external server.
The risks include data leakage, unauthorized access to system information, and potential exploitation of the affected application.
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.
The best course of action is to remove the package entirely, as there are no effective workarounds to mitigate the risks posed by the embedded malicious code.
