CVE-2024-39646 in Custom 404 Pro Plugin
Summary
by MITRE • 08/02/2024
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Kunal Custom 404 Pro custom-404-pro.This issue affects Custom 404 Pro: from n/a through <= 3.11.1.
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Analysis
by VulDB Data Team • 04/02/2026
This cross-site scripting vulnerability exists within the Kunal Custom 404 Pro plugin for WordPress, specifically impacting versions ranging from the initial release through version 3.11.1. The flaw represents a classic input sanitization failure that occurs during web page generation processes, allowing malicious actors to inject arbitrary JavaScript code into web pages viewed by other users. The vulnerability stems from insufficient validation and sanitization of user-supplied input parameters that are subsequently rendered in web page content without proper encoding or escaping mechanisms. This type of weakness falls under the Common Weakness Enumeration category CWE-79, which specifically addresses improper neutralization of input during web page generation, making it a direct implementation of the well-known XSS attack vector.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform session hijacking, deface websites, redirect users to malicious domains, or harvest sensitive information from authenticated users. When exploited, the XSS vulnerability allows threat actors to execute malicious scripts in the context of a victim's browser, potentially compromising user sessions and enabling persistent attacks against the affected WordPress installation. The vulnerability is particularly concerning because it affects the 404 error handling functionality of the website, which means that even when users encounter broken links or non-existent pages, they may unknowingly execute malicious code. This exploitation vector is especially dangerous as it can be triggered through normal browsing behavior without requiring user interaction beyond visiting a compromised page.
Security practitioners should consider this vulnerability in the context of the ATT&CK framework under the T1566 technique for initial access through social engineering, as the XSS attack can be delivered through phishing emails or compromised web content. The vulnerability also aligns with T1071.004 for application layer protocol usage, particularly HTTP traffic manipulation. Mitigation strategies should include immediate patching to version 3.11.2 or later, which contains the necessary input sanitization fixes. Additionally, administrators should implement Content Security Policy headers to limit script execution, employ web application firewalls for additional protection layers, and conduct regular security audits of plugin installations. The vulnerability highlights the critical importance of input validation and output encoding in web applications, particularly in error handling mechanisms where user input is often processed without proper sanitization. Organizations should also consider implementing automated monitoring for suspicious script injection attempts and maintain comprehensive backup strategies to quickly restore compromised systems.