CVE-2024-8799 is a reflected Cross-Site Scripting (XSS) vulnerability identified in the Custom Banners plugin for WordPress, developed by ghuger. This vulnerability exists in all versions up to and including 3.3 due to the improper handling of user input when generating web pages. Specifically, the plugin uses the WordPress function add_query_arg to manipulate URL query parameters without applying appropriate escaping or sanitization. This flaw allows an unauthenticated attacker to craft malicious URLs containing arbitrary JavaScript code. When a victim clicks on such a link, the injected script executes within the context of the victim's browser session on the affected site. The vulnerability is classified under CWE-79, which pertains to improper neutralization of input during web page generation. The attack vector is network-based (AV:N), requires no privileges (PR:N), but does require user interaction (UI:R). The scope is changed (S:C) because the vulnerability can affect resources beyond the vulnerable component, potentially impacting the entire site. The impact includes limited confidentiality and integrity loss (C:L, I:L) but no availability impact (A:N). Although no public exploits have been reported, the vulnerability poses a risk of session hijacking, credential theft, or malicious content injection, which can lead to phishing or defacement. The vulnerability was published on October 1, 2024, and has a CVSS 3.1 base score of 6.1, indicating medium severity. The lack of patches at the time of reporting underscores the need for immediate attention by site administrators.

The primary impact of CVE-2024-8799 is the potential compromise of user confidentiality and integrity on websites using the vulnerable Custom Banners plugin. Attackers can execute arbitrary JavaScript in the context of the victim’s browser, enabling theft of session cookies, credentials, or other sensitive information accessible via the browser. This can lead to account takeover, unauthorized actions on behalf of users, or distribution of malware through injected scripts. Although availability is not directly affected, the reputational damage and loss of user trust can be significant. Since the vulnerability requires user interaction, the attack surface depends on the ability to lure users into clicking malicious links, which can be facilitated via phishing campaigns. Organizations running WordPress sites with this plugin, especially those handling sensitive user data or financial transactions, face increased risk of data breaches and compliance violations. The vulnerability also increases the risk of further exploitation through chained attacks leveraging stolen credentials or session tokens.

1. Immediate mitigation involves updating the Custom Banners plugin to a fixed version once available from the vendor. Monitor official channels for patch releases. 2. Until a patch is released, implement Web Application Firewall (WAF) rules to detect and block suspicious query parameters containing script tags or typical XSS payloads targeting the plugin’s URL patterns. 3. Employ Content Security Policy (CSP) headers to restrict the execution of inline scripts and limit the sources of executable scripts, reducing the impact of injected scripts. 4. Educate users and administrators about the risks of clicking on untrusted links, especially those that appear to come from the affected site. 5. Regularly audit and sanitize all user inputs and URL parameters in custom code or plugins to prevent similar vulnerabilities. 6. Monitor logs for unusual URL access patterns or spikes in suspicious traffic that may indicate exploitation attempts. 7. Consider disabling or removing the Custom Banners plugin if it is not essential to reduce the attack surface.