CVE-2024-9204 is a reflected Cross-Site Scripting vulnerability identified in the Smart Custom 404 Error Page plugin for WordPress, developed by nerdpressteam. This plugin, widely used to customize 404 error pages, improperly handles user input from the $_SERVER['REQUEST_URI'] variable. Specifically, it fails to adequately sanitize and escape this input before embedding it into the generated error page, violating secure coding practices against CWE-79 (Improper Neutralization of Input During Web Page Generation). As a result, an attacker can craft a malicious URL containing executable JavaScript code within the URI. When a victim clicks this URL, the malicious script is reflected back and executed in their browser context. This attack vector requires no authentication but does require user interaction (clicking the link). The vulnerability affects all plugin versions up to and including 11.4.7. The CVSS 3.1 score of 6.1 indicates a medium severity, with the attack vector being network-based, no privileges required, user interaction required, and a scope change possible due to script execution in the user's browser. The impact primarily concerns confidentiality and integrity, as attackers can steal session cookies, perform actions on behalf of the user, or manipulate displayed content. No patches or fixes are currently linked, and no known exploits have been reported in the wild, but the vulnerability is publicly disclosed and should be addressed promptly.

The primary impact of CVE-2024-9204 is on the confidentiality and integrity of users interacting with affected WordPress sites. Successful exploitation allows attackers to execute arbitrary JavaScript in the context of the victim's browser, potentially leading to session hijacking, theft of sensitive information such as cookies or credentials, and unauthorized actions performed on behalf of the user. While availability is not directly affected, the reputational damage to organizations can be significant if users are exposed to phishing or malware delivery via the injected scripts. Since the vulnerability is reflected XSS, it requires user interaction, limiting automated exploitation but still posing a serious risk especially for sites with high traffic or sensitive user data. Organizations relying on the Smart Custom 404 Error Page plugin may face increased risk of targeted attacks, especially if attackers craft phishing campaigns leveraging this vulnerability. The scope of affected systems is broad given the plugin's usage in WordPress environments worldwide, particularly in small to medium businesses and personal websites that may not have rigorous security monitoring. The lack of an official patch at the time of disclosure increases the urgency for interim mitigations.

To mitigate CVE-2024-9204, organizations should first check for any official patches or updates from nerdpressteam and apply them immediately once available. In the absence of a patch, administrators can implement the following specific measures: 1) Disable or temporarily deactivate the Smart Custom 404 Error Page plugin until a fix is released. 2) Employ a Web Application Firewall (WAF) with rules to detect and block suspicious URI patterns containing script tags or typical XSS payloads targeting the 404 error page. 3) Implement Content Security Policy (CSP) headers that restrict the execution of inline scripts and untrusted sources, reducing the impact of injected scripts. 4) Sanitize and validate all user inputs at the server level, especially those reflected in error pages, by customizing or overriding the plugin’s error page rendering code if feasible. 5) Educate users and administrators about the risks of clicking unknown or suspicious links to reduce the chance of successful exploitation. 6) Monitor web server logs for unusual request patterns or repeated attempts to exploit the vulnerability. 7) Consider using security plugins that provide XSS protection or input filtering for WordPress sites. These targeted mitigations go beyond generic advice by focusing on the specific plugin behavior and attack vector.