CVE-2024-13992 is a cross-site scripting (XSS) vulnerability identified in Nagios XI, a widely used IT infrastructure monitoring product. The flaw exists in the page-missing.php script, which generates the 404 error page. This component fails to properly sanitize or escape user-supplied input embedded in the URL, allowing an attacker to inject malicious JavaScript code. When a victim clicks a specially crafted link leading to a non-existent page on a vulnerable Nagios XI instance, the injected script executes in the context of the Nagios XI web application. This can lead to session hijacking, credential theft, or unauthorized actions performed with the victim’s privileges. The vulnerability does not require authentication but does require user interaction, as the victim must visit the malicious URL. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:L), user interaction required (UI:P), and limited scope and impact on confidentiality, integrity, and availability (VC:N/VI:N/VA:N). No public exploits have been reported yet, but the vulnerability is publicly disclosed and patched in version 2024R1.1. The root cause is improper neutralization of input during web page generation, classified under CWE-79.

For European organizations, the impact of this vulnerability primarily concerns the security of Nagios XI web interfaces used for monitoring critical IT infrastructure. Successful exploitation could allow attackers to execute arbitrary scripts in the context of the Nagios XI domain, potentially leading to session hijacking, theft of sensitive monitoring data, or manipulation of monitoring dashboards. While the vulnerability does not directly compromise system availability or integrity, it can facilitate further attacks or unauthorized access if combined with other vulnerabilities or social engineering. Organizations relying heavily on Nagios XI for network and system monitoring may face operational risks if attackers leverage this XSS to disrupt monitoring or gain footholds. The medium severity reflects that exploitation requires user interaction and has limited direct impact, but the strategic importance of monitoring systems in European enterprises and critical infrastructure elevates the risk profile.

European organizations should immediately upgrade Nagios XI to version 2024R1.1 or later, where this vulnerability is patched. In addition to patching, organizations should implement strict input validation and output encoding on all user-supplied data within their Nagios XI customizations or integrations. Deploying a Content Security Policy (CSP) can help mitigate the impact of XSS by restricting the execution of unauthorized scripts. Network-level protections such as web application firewalls (WAFs) should be configured to detect and block suspicious URL patterns or script injections targeting the 404 page. Security awareness training should inform users about the risks of clicking untrusted links, especially those pointing to internal monitoring systems. Regular security audits and penetration testing of Nagios XI deployments can help identify residual or related vulnerabilities. Finally, monitoring logs for unusual access patterns to the 404 page may provide early detection of exploitation attempts.