CVE-2023-6735 is a high-severity privilege escalation vulnerability affecting the mk_tsm agent plugin in Checkmk versions prior to 2.2.0p18, 2.1.0p38, and 2.0.0p39. Checkmk is a widely used IT monitoring software developed by Checkmk GmbH. The vulnerability is classified under CWE-95, which involves improper neutralization of directives in dynamically evaluated code, commonly known as 'eval injection.' This flaw allows a local user with limited privileges to execute arbitrary code with elevated privileges by exploiting the way the mk_tsm plugin processes input. Specifically, the vulnerability arises because the plugin improperly handles dynamically evaluated code, enabling an attacker to inject malicious directives that the system executes. The CVSS v3.1 base score is 8.8, indicating a high severity level. The attack vector is local (AV:L), requiring low attack complexity (AC:L), and low privileges (PR:L) but no user interaction (UI:N). The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component. The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), indicating that exploitation can lead to full system compromise. Although no known exploits are currently reported in the wild, the vulnerability's nature and severity suggest that exploitation could allow an attacker to gain root or administrative privileges on the affected system, potentially leading to full control over the monitored infrastructure. This vulnerability is particularly critical because Checkmk is often deployed in enterprise environments to monitor critical IT infrastructure, making it a valuable target for attackers seeking to escalate privileges and move laterally within networks.

For European organizations, the impact of CVE-2023-6735 could be significant, especially for those relying on Checkmk for monitoring critical IT infrastructure such as data centers, cloud environments, and industrial control systems. Successful exploitation could allow an attacker to escalate privileges from a local user account to root or administrative levels, enabling them to manipulate monitoring data, disable alerts, or use the compromised system as a foothold for further attacks within the network. This could lead to data breaches, disruption of services, and loss of integrity in monitoring systems, which are essential for maintaining operational continuity and security compliance. Given the high impact on confidentiality, integrity, and availability, organizations could face regulatory penalties under GDPR if sensitive data is exposed or if service disruptions affect customers. Additionally, the ability to escalate privileges locally means that insider threats or attackers who have gained limited access could leverage this vulnerability to cause extensive damage.

To mitigate this vulnerability, European organizations should urgently apply the patches released by Checkmk in versions 2.2.0p18, 2.1.0p38, and 2.0.0p39 or later. If immediate patching is not feasible, organizations should restrict local access to systems running vulnerable versions of Checkmk, limiting user permissions to only those necessary for operational tasks. Implement strict access controls and monitoring on systems hosting the mk_tsm agent plugin to detect any unusual activity indicative of exploitation attempts. Additionally, organizations should audit their Checkmk configurations to ensure that no untrusted input is processed by the mk_tsm plugin and consider disabling or isolating the plugin if it is not essential. Employing endpoint detection and response (EDR) solutions to monitor for suspicious local privilege escalation behaviors can provide early warning. Finally, maintain robust logging and alerting mechanisms to detect any unauthorized privilege escalations promptly.