CVE-2025-56394 is a high-severity buffer overflow vulnerability identified in Free5gc version 4.0.1, an open-source 5G core network implementation. The vulnerability arises from improper validation of the 5GS mobile identity within the Access and Mobility Management Function (AMF) component. Specifically, the AMF fails to correctly validate the length or structure of the 5GS mobile identity, leading to a slice reference overflow condition. This type of buffer overflow (classified under CWE-122) can cause memory corruption, potentially resulting in denial of service (DoS) conditions or enabling an attacker to execute arbitrary code or disrupt the availability of the affected system. The vulnerability can be exploited remotely over the network without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). Although the impact on confidentiality and integrity is not indicated, the vulnerability has a significant impact on availability, with a CVSS score of 7.5 (high severity). No known exploits are currently reported in the wild, and no patches have been linked yet, highlighting the need for proactive mitigation and monitoring. Given Free5gc's role as a 5G core network component, exploitation could disrupt mobile network services relying on this software, affecting network operators and their subscribers.

For European organizations, particularly telecommunications providers deploying Free5gc 4.0.1 or derivatives thereof, this vulnerability poses a substantial risk to the availability of 5G network services. Disruption of the AMF could lead to denial of service for mobile subscribers, impacting critical communications infrastructure, emergency services, and enterprise connectivity. The 5G core network is foundational for emerging technologies such as IoT, autonomous vehicles, and smart city applications; thus, service interruptions could have cascading effects on various sectors including transportation, healthcare, and manufacturing. Additionally, network operators may face regulatory scrutiny under the EU's NIS2 Directive and GDPR if service disruptions affect data processing or availability. The lack of authentication and user interaction requirements means attackers can potentially launch attacks remotely, increasing the threat surface. While no known exploits exist yet, the public disclosure of this vulnerability necessitates immediate attention to prevent exploitation attempts, especially as threat actors often develop exploits rapidly after disclosure.

Organizations should first identify any deployments of Free5gc 4.0.1 within their 5G core network infrastructure. Given the absence of an official patch, immediate mitigations include implementing network-level protections such as strict ingress filtering and anomaly detection to identify malformed 5GS mobile identity messages targeting the AMF. Deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with custom signatures to detect abnormal slice reference lengths or malformed packets can help mitigate exploitation attempts. Network segmentation should be enforced to isolate the AMF from less trusted network segments. Operators should engage with the Free5gc community and vendors for updates or patches and plan for rapid deployment once available. Additionally, monitoring AMF logs and network traffic for unusual behavior or crashes can provide early warning signs of exploitation attempts. Conducting regular security assessments and penetration testing focused on 5G core components will help identify residual risks. Finally, updating incident response plans to include scenarios involving 5G core network component compromise is recommended.