CVE-2025-31394 identifies a stored cross-site scripting (XSS) vulnerability in the More Mime Type Filters plugin for web applications, specifically versions up to 0.3. The vulnerability is caused by improper neutralization of user-supplied input during the generation of web pages, which allows attackers to inject malicious JavaScript code that is stored persistently on the server. When other users or administrators access the affected pages, the malicious script executes in their browsers, potentially leading to session hijacking, credential theft, or unauthorized actions within the application context. The plugin, developed by Kailey (trepmal), is used to extend MIME type filtering capabilities, likely in content management systems such as WordPress. The lack of a CVSS score indicates this is a newly published vulnerability as of April 9, 2025, with no public exploit code yet. However, stored XSS vulnerabilities are generally considered severe due to their persistent nature and potential for widespread impact. The vulnerability does not require authentication to exploit, increasing its risk profile. No official patches or mitigations have been linked yet, emphasizing the need for immediate attention from users of the affected plugin versions.

The stored XSS vulnerability in More Mime Type Filters can have severe consequences for organizations worldwide. Attackers can leverage this flaw to execute arbitrary JavaScript in the browsers of users who visit affected pages, leading to theft of sensitive information such as session cookies, personal data, or administrative credentials. This can result in unauthorized access, data breaches, defacement, or further compromise of the web application and its backend systems. The persistent nature of stored XSS means the malicious payload remains active until the vulnerability is remediated, increasing the window of opportunity for attackers. For organizations relying on this plugin, especially those handling sensitive user data or financial transactions, the impact includes reputational damage, regulatory penalties, and operational disruption. Additionally, attackers could use the vulnerability as a foothold for more advanced attacks, including lateral movement within the network or supply chain attacks if the compromised site is trusted by other systems.

To mitigate CVE-2025-31394, organizations should immediately identify if they are using the More Mime Type Filters plugin version 0.3 or earlier. Since no official patches are currently available, temporary mitigations include disabling or uninstalling the plugin until a fix is released. Web application firewalls (WAFs) can be configured to detect and block typical XSS payloads targeting the plugin’s input fields. Developers should review and sanitize all user inputs rigorously, employing context-aware output encoding to neutralize scripts before rendering. Implementing Content Security Policy (CSP) headers can help restrict the execution of unauthorized scripts in browsers. Regularly monitoring web application logs for suspicious input patterns and unusual user behavior can aid early detection of exploitation attempts. Once a patch is released, prompt application of updates is critical. Additionally, educating administrators and users about the risks of clicking on suspicious links or inputs can reduce the likelihood of successful exploitation.