The vulnerability identified as CVE-2025-53533 affects the Pi-hole Admin Interface, a web-based management tool for the Pi-hole network-level ad and tracker blocking application. Versions 6.2.1 and earlier are susceptible to a reflected cross-site scripting (XSS) attack due to improper neutralization of user input in the 404 error page. Specifically, the requested URL path is embedded directly into the class attribute of the body tag without proper sanitization or escaping. An attacker can exploit this by crafting a malicious URL containing an onload attribute or other JavaScript payload within the path segment. When a victim accesses this URL, the injected JavaScript executes in their browser context, potentially allowing the attacker to steal cookies, perform actions on behalf of the user, or deliver further malicious payloads. The vulnerability does not require any privileges or authentication, but it does require the victim to click or visit the malicious link. The issue has been addressed in Pi-hole version 6.3 by properly sanitizing the URL path before rendering it in the error page. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges required, user interaction required, and limited scope impact, resulting in a medium severity score of 5.1.

For European organizations, the impact of this vulnerability can be significant depending on the deployment of Pi-hole within their networks. Pi-hole is commonly used in corporate, educational, and home environments to block ads and trackers at the DNS level. Exploitation of this XSS vulnerability could allow attackers to execute arbitrary JavaScript in the context of the Pi-hole admin interface, potentially leading to session hijacking, theft of administrative credentials, or manipulation of Pi-hole settings. This could degrade network security, allow bypassing of ad-blocking controls, or facilitate further lateral movement within the network. Since the vulnerability requires user interaction, phishing or social engineering campaigns could be used to lure administrators or users into clicking malicious links. The medium CVSS score reflects moderate risk, but the exposure of administrative interfaces to the internet or untrusted networks increases the potential impact. Organizations relying on Pi-hole for network security and privacy should consider this vulnerability a priority for patching to maintain integrity and availability of their DNS filtering services.

European organizations should immediately upgrade all Pi-hole Admin Interface installations to version 6.3 or later, where the vulnerability is patched. If immediate upgrading is not feasible, organizations should implement strict access controls to restrict access to the Pi-hole admin interface, such as VPN-only access or IP whitelisting, to reduce exposure to untrusted users. Web application firewalls (WAFs) can be configured to detect and block suspicious URL patterns that include script injection attempts in the path. Educate users and administrators about the risks of clicking unsolicited or suspicious links, especially those purporting to be related to network management tools. Regularly audit Pi-hole logs for unusual access patterns or error page requests that may indicate attempted exploitation. Additionally, consider deploying Content Security Policy (CSP) headers on the Pi-hole web interface to limit the impact of any potential XSS by restricting script execution sources. Finally, maintain an up-to-date inventory of Pi-hole deployments to ensure all instances are patched promptly.