CVE-2024-8799 in Custom Banners Plugin
Summary
by MITRE • 10/01/2024
The Custom Banners plugin for WordPress is vulnerable to Reflected Cross-Site Scripting due to the use of add_query_arg without appropriate escaping on the URL in all versions up to, and including, 3.3. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link.
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Analysis
by VulDB Data Team • 03/09/2025
The Custom Banners plugin for WordPress presents a critical security vulnerability classified as reflected cross-site scripting that affects all versions up to and including 3.3. This flaw resides in the plugin's handling of URL parameters through the add_query_arg function without proper escaping mechanisms. The vulnerability creates a pathway for unauthenticated attackers to inject malicious scripts into web pages that will execute when users navigate to specifically crafted URLs. The attack vector exploits the plugin's failure to sanitize user input within URL construction, making it particularly dangerous as it requires no authentication credentials from the attacker to exploit.
The technical implementation of this vulnerability stems from the plugin's improper use of WordPress's add_query_arg function which is designed to add query arguments to URLs but does not automatically escape output for safe rendering in HTML contexts. When the plugin processes user-supplied parameters through this function and subsequently renders them in web pages without appropriate sanitization, it creates an environment where malicious JavaScript code can be injected and executed in the context of a victim's browser. This pattern aligns with CWE-79, which specifically addresses cross-site scripting vulnerabilities arising from insufficient output escaping, and represents a classic reflected XSS attack scenario where the malicious payload is reflected back to the user through the application's response.
The operational impact of this vulnerability extends beyond simple script execution as it can enable sophisticated attack chains targeting WordPress administrators and users. An attacker could craft malicious URLs containing payloads designed to steal session cookies, redirect users to phishing sites, or perform actions on behalf of authenticated users within the WordPress environment. The vulnerability's accessibility to unauthenticated users means that any user visiting a maliciously crafted link could become compromised, making it particularly dangerous for sites with high user interaction or public-facing content. This type of vulnerability falls under ATT&CK technique T1566.001, which describes the use of malicious links to deliver initial access payloads, and represents a common vector for establishing persistent access or executing further exploitation techniques.
Mitigation strategies for this vulnerability require immediate action including updating to the latest plugin version where the XSS flaw has been patched, implementing proper input validation and output escaping mechanisms, and deploying web application firewalls that can detect and block malicious script injection attempts. Administrators should also consider implementing Content Security Policy headers to limit script execution contexts and monitor for suspicious URL patterns in their web server logs. The vulnerability demonstrates the critical importance of proper input sanitization and output escaping in web applications, particularly when dealing with user-supplied parameters that may be reflected back to users. Organizations should conduct thorough security assessments of their WordPress installations to identify other potential XSS vulnerabilities in plugins and themes, as this represents a common class of weakness that can lead to significant compromise of web applications and user data.