WordPress Plugin Flaw Exposes 200,000+ Websites to XSS Attacks

Over 200,000 websites have been left vulnerable to Cross-Site Scripting (XSS) attacks due to a flaw in the Ultimate Member plugin for WordPress.

This vulnerability, discovered by a researcher known as stealthcopter, underscores the ongoing risks in the digital ecosystem and highlights the critical role of cybersecurity firms like Wordfence in safeguarding the web.

Discovery and Disclosure

During the Wordfence Bug Bounty Extravaganza, stealthcopter submitted a report detailing an unauthenticated stored XSS vulnerability in the Ultimate Member plugin.

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This plugin, designed for user profile, registration, and membership management on WordPress sites, boasts over 200,000 active installations, making the potential impact of this vulnerability substantial.

Wordfence, a leading security service for WordPress websites, awarded Stealthcopter a $563 bounty for this discovery.

The company’s swift action in validating and disclosing the vulnerability to the Ultimate Member team exemplifies its commitment to securing the web. By March 6, 2024, a patch was released, mitigating the risk for millions of web users.

Technical Breakdown

The vulnerability, CVE-2024-2123, allows attackers to inject malicious scripts into web pages via several parameters in Ultimate Member plugin versions up to and including 2.8.3.

This flaw arises from insufficient input sanitization and output escaping, particularly in the plugin’s member directory list functionality.

An examination of the plugin’s code revealed that user display names were displayed unescaped in template files, making it possible for attackers to provide a name containing a malicious script during registration as an unauthenticated user.

This could lead to a range of malicious activities, including adding administrative users, redirecting harmful sites, and injecting backdoors into theme and plugin files.

The revelation of this vulnerability has highlighted the importance of regular updates and vigilant security practices for website administrators.

Websites running outdated versions of the Ultimate Member plugin were at risk of being exploited by unauthenticated attackers, potentially leading to unauthorized administrative access and further compromise.

Wordfence has been at the forefront of addressing this vulnerability, providing immediate protection to its users through the Wordfence firewall’s built-in XSS protection.

This includes customers of Wordfence Premium, Wordfence Care, and Wordfence Response, as well as users of the free version of the plugin.

The swift identification, reporting, and patching of the XSS vulnerability in the Ultimate Member plugin testifies to the collaborative efforts between cybersecurity researchers and developers in protecting the digital landscape.

Wordfence’s role in this process not only highlights its commitment to web security but also reminds us of the importance of proactive security measures and regular software updates.

WordPress site owners are urged to update their installations to the latest patched version of Ultimate Member (2.8.4) to safeguard against potential exploits.

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