CVE-2025-12206 identifies a NULL pointer dereference vulnerability in Kamailio version 5.5, specifically within the rve_is_constant function located in src/core/rvalue.c. This flaw arises when the function attempts to dereference a NULL pointer, leading to a potential denial of service by crashing the Kamailio SIP server process. The vulnerability requires an attacker to have local access to the system and the ability to manipulate Kamailio configuration files, which is a significant barrier to exploitation. No remote exploitation vector is available, and no user interaction or authentication bypass is involved beyond local privileges. The vulnerability was disclosed on October 27, 2025, with a CVSS 4.8 (medium) score reflecting its limited attack vector and impact. Although exploit code has been published, the practical exploitation scenario is constrained by the need to alter configuration files, which are typically protected and require elevated permissions. The vendor has not issued any patches or advisories, leaving organizations reliant on their own mitigations. Kamailio is widely used in telecommunications infrastructure for SIP signaling, so the vulnerability could impact VoIP services if exploited. However, the requirement for local access and configuration manipulation reduces the likelihood of widespread exploitation. Organizations should monitor for updates and consider hardening local access and configuration management to mitigate this risk.

For European organizations, the primary impact of CVE-2025-12206 is the potential for denial of service on Kamailio SIP servers, which could disrupt VoIP communications and related telephony services. This may affect enterprises, service providers, and telecom operators relying on Kamailio 5.5 for SIP signaling. The requirement for local access and configuration file manipulation limits the risk of remote attacks but elevates the importance of internal security controls. Insider threats or compromised local accounts could exploit this vulnerability to cause service outages. Disruption of telephony services can have operational and reputational consequences, especially for critical infrastructure and emergency communication systems. The lack of vendor response and patches increases the risk exposure until mitigations are implemented. European telecom operators and enterprises with sensitive communications infrastructure should prioritize assessing their Kamailio deployments and access controls to prevent exploitation.

1. Restrict local access to systems running Kamailio 5.5 to trusted administrators only, employing strong authentication and access controls. 2. Harden file system permissions to prevent unauthorized modification of Kamailio configuration files, ensuring only privileged users can edit these files. 3. Implement monitoring and alerting for unauthorized changes to configuration files and unusual local activity on Kamailio servers. 4. Consider deploying Kamailio behind additional layers of security such as network segmentation and host-based firewalls to limit local access vectors. 5. Regularly audit user accounts and privileges on Kamailio hosts to detect and remove unnecessary local accounts. 6. Stay informed on vendor advisories and community updates for patches or workarounds addressing this vulnerability. 7. If feasible, test upgrading to newer Kamailio versions that may have addressed this issue or provide enhanced security features. 8. Develop incident response plans specifically for telephony service disruptions to minimize operational impact if exploitation occurs.