CVE-2024-13993 is a reflected cross-site scripting vulnerability identified in Nagios XI, a widely used IT infrastructure monitoring solution. The vulnerability exists in versions prior to 2024R1.1.2 and is triggered via the login page. Specifically, the login page fails to properly validate or escape user-supplied input that is reflected back in the page content. This improper neutralization of input (CWE-79) allows an attacker to craft a malicious URL containing JavaScript payloads. When a victim using an older or legacy web browser visits this URL, the injected script executes within the context of the Nagios XI web application origin. This can lead to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. The vulnerability is less effective or mitigated in modern browsers due to improved XSS protections such as Content Security Policy (CSP) enforcement and stricter input handling. The CVSS 4.0 vector indicates the attack can be performed remotely (AV:N), with low attack complexity (AC:L), no privileges required (PR:N), but requires user interaction (UI:A). The vulnerability does not impact confidentiality, integrity, or availability directly (VC:N, VI:N, VA:N), but the scope is limited (S:L). No known exploits have been reported in the wild yet, but the presence of this vulnerability in a critical monitoring tool poses a risk if exploited. The lack of a patch link suggests that remediation involves upgrading to Nagios XI 2024R1.1.2 or later once available.

For European organizations, the impact of CVE-2024-13993 can be significant, especially for those relying on Nagios XI for critical infrastructure monitoring. Successful exploitation could allow attackers to execute arbitrary scripts in the context of the Nagios XI web interface, potentially leading to session hijacking, theft of sensitive monitoring data, or manipulation of monitoring configurations. This could degrade the integrity and confidentiality of monitoring data and alerts, impairing incident response and operational awareness. Organizations using legacy browsers or with users who have not adopted modern browser versions are at higher risk. Additionally, attackers could leverage this vulnerability as a foothold for further attacks within the network. Given Nagios XI’s role in monitoring IT infrastructure, disruption or compromise could indirectly affect availability of monitored services. The medium CVSS score reflects moderate risk, but the potential for targeted phishing campaigns exploiting this vulnerability could increase its impact. European sectors such as finance, energy, and government, which rely heavily on Nagios XI, may face elevated risks.

1. Upgrade Nagios XI to version 2024R1.1.2 or later as soon as the patch is available to ensure the vulnerability is fully remediated. 2. Enforce the use of modern, up-to-date browsers among all users accessing Nagios XI to leverage built-in XSS protections. 3. Implement strict input validation and output encoding on the login page and other user input fields to prevent injection of malicious scripts. 4. Deploy Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts within the Nagios XI web application. 5. Educate users about the risks of clicking on suspicious links, especially those received via email or other communication channels. 6. Monitor web server logs for unusual URL patterns or repeated attempts to exploit XSS vectors. 7. Consider using web application firewalls (WAFs) with rules designed to detect and block reflected XSS attacks targeting Nagios XI. 8. Conduct regular security assessments and penetration testing focused on web application vulnerabilities in Nagios XI deployments.