CVE-2024-13722 identifies a reflected cross-site scripting (XSS) vulnerability in the NagVis visualization component of the Checkmk monitoring software, specifically in versions NagVis 1.9.40 and Checkmk 2.3.0p2. The vulnerability arises due to improper neutralization of user-supplied input during web page generation, classified under CWE-79. An attacker can craft a specially designed URL containing malicious JavaScript code that, when clicked by a user, executes within the context of the victim's browser session. This execution can lead to theft of session cookies, redirection to malicious sites, or execution of unauthorized actions on behalf of the user. The vulnerability affects both authenticated and unauthenticated users, broadening the scope of potential targets. The CVSS 3.1 base score is 5.4, reflecting a medium severity with attack vector as network, low attack complexity, requiring low privileges and user interaction, and impacting confidentiality and integrity with no availability impact. No public exploits have been reported yet, but the vulnerability's presence in monitoring infrastructure software like Checkmk NagVis is concerning due to the sensitive nature of monitoring data and potential access to internal network information. The lack of available patches at the time of reporting necessitates immediate attention to mitigation strategies.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of monitoring data and user sessions within Checkmk NagVis environments. Successful exploitation could allow attackers to hijack user sessions, steal credentials, or perform unauthorized actions within the monitoring platform, potentially leading to further network reconnaissance or lateral movement. Given that NagVis is used for visualizing network and system monitoring data, compromise could expose sensitive operational information or disrupt trust in monitoring outputs. Organizations relying on Checkmk NagVis for critical infrastructure monitoring may face increased risk of targeted attacks, especially if attackers leverage this XSS flaw as an initial foothold. The vulnerability's ability to affect unauthenticated users increases exposure, particularly in environments where NagVis interfaces are accessible externally or to a broad user base. While no availability impact is noted, the indirect consequences of compromised monitoring data integrity could affect incident response and operational decision-making.

European organizations should immediately assess their use of Checkmk NagVis versions 1.9.40 and Checkmk 2.3.0p2 and plan for prompt upgrades once patches become available. In the interim, implement strict input validation and output encoding on all user-supplied data within NagVis interfaces to prevent script injection. Employ web application firewalls (WAFs) with rules targeting common XSS attack patterns to block malicious payloads. Restrict access to NagVis interfaces to trusted networks and authenticated users where possible, reducing exposure to unauthenticated attacks. Educate users to avoid clicking suspicious links related to NagVis and monitor logs for unusual access patterns or attempted exploitation. Consider deploying Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in browsers accessing NagVis. Regularly review and update security configurations and conduct penetration testing focused on web application vulnerabilities in monitoring tools. Finally, maintain vigilance for vendor updates and advisories to apply official patches promptly.