CVE-2025-58124 identifies a vulnerability in the Checkmk Exchange plugin check-mk-api version 2.2, related to improper certificate validation classified under CWE-295. This weakness allows an attacker who can position themselves as a man-in-the-middle (MitM) to intercept traffic between the client and the API server. The vulnerability arises because the plugin fails to correctly validate TLS certificates, potentially accepting invalid or malicious certificates. This flaw undermines the confidentiality and integrity of the data transmitted, as attackers can eavesdrop or alter communications without detection. The CVSS 4.0 base score of 6.9 reflects a medium severity, with network attack vector, no privileges required, no user interaction, and partial impact on integrity. The vulnerability affects version 2.2 of Checkmk, a widely used IT infrastructure monitoring tool, which is critical for operational visibility and alerting. Although no public exploits are known, the vulnerability's presence in a monitoring tool increases risk, as attackers could manipulate monitoring data or gain insights into network operations. The vulnerability was reserved and published in August 2025, with no patches currently listed, indicating the need for immediate attention from users and vendors.

For European organizations, this vulnerability poses a risk to the confidentiality and integrity of monitoring data transmitted via the Checkmk API. Successful exploitation could allow attackers to intercept sensitive operational data, manipulate monitoring results, or disrupt alerting mechanisms, potentially delaying incident response. This is particularly critical for sectors relying heavily on IT infrastructure monitoring, such as finance, telecommunications, energy, and government services. The ability to perform MitM attacks without authentication or user interaction increases the risk, especially in environments where network segmentation or encryption is insufficient. Given the widespread use of Checkmk in Europe, especially in Germany, France, and the UK, the impact could be significant, affecting critical infrastructure and enterprise environments. The vulnerability could also facilitate further lateral movement or reconnaissance by adversaries within compromised networks.

To mitigate CVE-2025-58124, organizations should first verify if they are running Checkmk Exchange plugin check-mk-api version 2.2 and plan for immediate upgrade once a patch is released. In the absence of a patch, enforce strict TLS certificate validation policies at the network level, including the use of certificate pinning or mutual TLS where feasible. Network segmentation and the use of VPNs or secure tunnels can reduce exposure to MitM attacks. Monitoring network traffic for anomalies and employing intrusion detection systems capable of identifying MitM patterns is recommended. Additionally, organizations should audit their monitoring infrastructure to ensure no unauthorized certificates are trusted and review API access logs for suspicious activity. Engaging with Checkmk support or community channels for updates and workarounds is advisable. Finally, educating network administrators about the risks of improper certificate validation and MitM attacks will enhance overall security posture.