CVE-2025-28917 identifies a stored Cross-site Scripting (XSS) vulnerability in the Custom Smilies plugin by crazyloong, affecting all versions up to 2.9.2. The vulnerability stems from improper neutralization of user-supplied input during web page generation, which allows attackers to inject malicious JavaScript code that is stored persistently on the server. When other users access pages containing the injected payload, the malicious script executes in their browsers within the context of the vulnerable site. This can lead to theft of session cookies, user impersonation, defacement, or delivery of further malware. The vulnerability does not require authentication or user interaction beyond visiting the affected page, increasing its exploitation potential. Although no public exploits have been reported, the nature of stored XSS makes it a critical concern for websites using this plugin. The affected product is commonly used in forums and content management systems to enhance user experience with custom emoticons. The lack of a CVSS score necessitates an assessment based on impact and exploitability, which indicates a high severity due to the broad scope and ease of exploitation. The vulnerability was published on March 26, 2025, and no official patches have been linked yet, emphasizing the need for immediate attention from administrators.

The impact of CVE-2025-28917 can be significant for organizations running websites that utilize the Custom Smilies plugin. Successful exploitation allows attackers to execute arbitrary scripts in the browsers of site visitors, potentially leading to session hijacking, unauthorized actions performed on behalf of users, theft of sensitive information, and distribution of malware. This undermines user trust and can result in reputational damage, regulatory penalties, and financial losses. Since the vulnerability is stored XSS, the malicious payload persists on the server, increasing the risk of widespread compromise. Attackers can target both end-users and administrators, potentially escalating privileges or gaining deeper access to the web application. The vulnerability affects the confidentiality and integrity of user data and can disrupt availability if used in conjunction with other attacks. Organizations with high-traffic websites or those handling sensitive user information are particularly vulnerable to the consequences of this exploit.

To mitigate CVE-2025-28917, organizations should first monitor official sources for patches or updates from the crazyloong project and apply them immediately upon release. In the absence of an official patch, administrators should implement strict input validation to sanitize all user inputs related to custom smilies, ensuring that scripts or HTML tags are not accepted. Employing output encoding techniques, such as HTML entity encoding, before rendering user-supplied content on web pages can prevent script execution. Web Application Firewalls (WAFs) can be configured to detect and block common XSS payloads targeting this plugin. Additionally, security teams should conduct regular code reviews and penetration testing focused on input handling in the plugin. Educating users about the risks of clicking suspicious links and maintaining up-to-date browser security settings can reduce the impact of successful exploits. Finally, logging and monitoring for unusual activity related to the plugin can help detect exploitation attempts early.