Malicious Code Injection in contoso-login-sim-loader: A Security Threat
Summary
MAL-2026-17322: Malicious code in contoso-login-sim-loader (npm). Affects contoso-login-sim-loader versions 1.0.1. No fix is published. How to fix ↓
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Background
The package 'contoso-login-sim-loader' is an npm library designed to act as a client-side asset loader, purportedly rendering a self-contained UI component when included via a script tag. However, it is fundamentally flawed as it ships a single, large browser script that is entirely encrypted and obfuscated, making it impossible to audit or verify its contents without executing it. This design raises significant security concerns, especially as it can embed malicious JavaScript into web pages, potentially compromising user data.
Vulnerability Detail
The vulnerability originates from the package's design, which includes an RC4-encrypted base64 blob that is decrypted at runtime. This script employs anti-analysis techniques to evade detection, such as aborting execution when developer tools are open and suppressing console logging. As a result, any website that includes this package unwittingly embeds attacker-controlled JavaScript into its pages, which can lead to credential harvesting and other malicious activities. The lack of transparency and documentation further exacerbates the risk, as users cannot ascertain the safety of the code being executed in their browsers.
How To Fix
This package is malicious. Remove it and rotate any credentials it could have accessed.
npm uninstall contoso-login-sim-loaderIf it arrived as a transitive dependency, remove the package that pulled it in, then reinstall.
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Workaround
Currently, there are no effective workarounds to mitigate the risks posed by this malicious package. The best course of action is to avoid using 'contoso-login-sim-loader' altogether and to ensure that your application does not include any unverified scripts.
Conclusion
The 'contoso-login-sim-loader' package poses a significant security threat due to its embedded malicious code. Users are strongly advised to remove this package from their projects and to utilize tools like Vulert to monitor for vulnerabilities in their applications. Ensuring the integrity of third-party packages is crucial for maintaining secure software environments.
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FAQ
It is an npm package that claims to be a client-side asset loader but is actually designed to inject malicious code into web pages.
The package contains an encrypted script that is decrypted at runtime, allowing attackers to execute arbitrary JavaScript in the context of the user's browser.
Using this package can lead to serious security issues, including credential theft and unauthorized access to user data.
You can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time. Visit Vulert Scanner to check your application without signing up.
Immediately remove the package from your project and replace it with a trusted alternative to mitigate any security risks.
