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In recent cybersecurity news, Sucuri has raised alarms over the growing trend of attackers exploiting WordPress must-use plugins (mu-plugins) to hide malware, ensuring persistent control over compromised websites. These mu-plugins are unique in that they auto-load on every page without needing activation, and are not visible in the standard plugin list, making them the perfect location for attackers to deploy backdoors undetected. This stealthy approach is a significant concern for website administrators.
the Threat
In February, Sucuri published a detailed report warning website administrators about the increasing exploitation of WordPress mu-plugins by threat actors. These plugins automatically load on every page, without requiring user activation, making them a hidden but persistent threat vector. As a result, attackers can exploit the mu-plugins directory to plant backdoors that evade detection by website administrators.
The report highlights a series of malicious tactics used by attackers, including obfuscated PHP scripts and functions like eval(), which execute arbitrary code silently. These hidden scripts are often used to manipulate website behavior, redirect users to malicious sites, and inject spam for SEO manipulation. The specific directory targeted by attackers, /wp-content/uploads/2024/12/, was used to store hidden payloads, which could then be executed remotely.
The types of malware identified by Sucuri include fake update redirects, web shells for complete site control, and spam injectors that hijack content. One notable example is a redirect script disguised as a legitimate WordPress function, which selectively redirects visitors while avoiding bots and administrators. This strategy ensures the malware remains undetected for a longer period.
Additionally, researchers found that these types of attacks can cause elevated server resource usage and unexpected file modifications. Common indicators of infection include unusual website behavior, such as unauthorized redirections or increased resource consumption. Attackers use these persistent backdoors for monetization, SEO manipulation, and other malicious activities.
What Undercode Say:
The rising trend of attackers targeting the mu-plugins directory underscores a significant shift in WordPress security. Traditionally, attackers would rely on more obvious routes like infected themes or plugins that could be easily deactivated or removed by site administrators. However, the exploitation of mu-plugins presents a much more insidious threat, as these plugins are hidden from the standard WordPress interface and are loaded automatically with every page.
One of the key reasons attackers are increasingly targeting mu-plugins is their ability to provide stealthy persistence. Because these plugins are automatically loaded with every page request, they remain active on the site without needing any user interaction. This persistence is crucial for attackers seeking to maintain long-term access to a compromised website.
The malware discovered by Sucuri relies on different techniques to achieve this persistence. For example, the fake update redirect malware is designed to mislead users into thinking they are receiving a legitimate update, when in fact, they are being redirected to a malicious website. This type of attack can lead to data theft, further infections, and a tarnished reputation for the targeted website.
On the other hand, the Remote Code Execution Webshell attack offers attackers complete control over the compromised website. By using functions like cURL, attackers can execute arbitrary PHP scripts remotely, enabling them to inject additional malicious code and extend the life of their infections. The ability to modify a site without directly altering the compromised file makes this type of attack especially dangerous.
Spam injection attacks, such as the one identified in the custom-js-loader.php file, manipulate site content for malicious purposes. These attacks typically replace legitimate images with explicit content or hijack links to open malicious popups. While these actions are harmful to a site’s reputation, they also serve to drive malicious traffic and generate profits for the attackers.
Another concerning aspect of these attacks is the variety of ways in which they are introduced. Sucuri speculates that attackers may gain access through vulnerable plugins, themes, compromised admin credentials, or poorly secured hosting environments. Once the attackers have access, they can upload and execute their malicious files, often without the website owner’s knowledge.
In light of these findings, it is clear that website administrators must be proactive in their security practices. Regular security monitoring, file integrity checks, and the implementation of web application firewalls (WAFs) are crucial to preventing these types of infections. Furthermore, keeping software updated and regularly auditing plugins and themes for vulnerabilities can significantly reduce the risk of such attacks.
Fact Checker Results
- Targeted Exploits: The mu-plugins directory is a growing concern for WordPress websites, offering attackers a way to maintain persistent, undetected access.
- Malware Methods: Attackers are using obfuscated PHP and cURL functions to execute hidden payloads and dynamically inject new malware, ensuring their presence remains undetected.
- Security Measures: To protect against such attacks, regular security practices such as monitoring and WAF implementation are crucial to safeguarding WordPress sites.
References:
Reported By: https://securityaffairs.com/176083/malware/wordpress-malware-in-the-mu-plugins-directory.html
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