CVE-2025-12206 is a vulnerability identified in Kamailio version 5.5, specifically within the function rve_is_constant located in src/core/rvalue.c. The flaw manifests as a null pointer dereference, which occurs when the function attempts to access or manipulate memory through a pointer that has not been properly initialized or has been set to null. This leads to a crash of the Kamailio process, resulting in a denial of service (DoS) condition. Exploitation requires local access with low privileges (PR:L) and no user interaction or authentication beyond local access is necessary. The attack vector is local, meaning an attacker must have some form of access to the host running Kamailio to trigger the vulnerability. The CVSS 4.0 base score is 4.8, reflecting a medium severity level due to the limited attack vector and impact scope. The vulnerability does not affect confidentiality or integrity but impacts availability by causing service interruptions. Although an exploit has been published, there are no confirmed reports of active exploitation in the wild. The vendor was notified early but has not issued any response or patch, leaving systems exposed. Kamailio is an open-source SIP server widely used in VoIP infrastructures, making this vulnerability relevant to organizations relying on SIP communications. The lack of patch availability necessitates alternative mitigation strategies until an official fix is released.

The primary impact of CVE-2025-12206 is on the availability of Kamailio-based SIP services. Successful exploitation causes the Kamailio process to crash, resulting in denial of service and disruption of VoIP communications. For European organizations, this can lead to significant operational impacts, especially for telecom providers, call centers, and enterprises relying on SIP for internal and external communications. Service outages may affect customer experience, business continuity, and emergency communication capabilities. Since the exploit requires local access, the risk is elevated in environments where attackers can gain initial footholds, such as through compromised user accounts or insider threats. The absence of vendor patches increases exposure duration, potentially allowing attackers to leverage this vulnerability as part of multi-stage attacks. The impact on confidentiality and integrity is minimal, but availability degradation can have cascading effects on dependent services and business operations.

Given the lack of an official patch, European organizations should implement the following mitigations: 1) Restrict local access to Kamailio servers by enforcing strict access controls, limiting user accounts with shell or command execution privileges. 2) Employ host-based intrusion detection and prevention systems (HIDS/HIPS) to monitor for suspicious activity and attempts to exploit the vulnerability. 3) Use containerization or sandboxing techniques to isolate Kamailio processes, minimizing the impact of crashes on the broader system. 4) Regularly audit and harden system configurations to reduce the attack surface, including disabling unnecessary services and enforcing least privilege principles. 5) Monitor Kamailio logs and system stability to detect early signs of exploitation attempts. 6) Prepare incident response plans to quickly recover from potential service disruptions. 7) Stay informed on vendor communications and community advisories for forthcoming patches or workarounds. 8) Consider upgrading to newer Kamailio versions if they become available and are confirmed to be unaffected by this vulnerability.