The vulnerability identified as CVE-2025-65562 affects the free5GC User Plane Function (UPF), a critical component in 5G core networks responsible for handling user data traffic. The flaw arises from a lack of bounds checking on the SEID (Session Endpoint Identifier) when processing PFCP (Packet Forwarding Control Protocol) Session Deletion Requests. Specifically, an attacker can send a PFCP message with an abnormally large SEID value (e.g., 0xFFFFFFFFFFFFFFFF). This value, when converted from an unsigned 64-bit integer (uint64) to a signed integer (int) in the Go programming language, causes an integer underflow. The underflow results in a negative index used to access the session array (n.sess) in the functions LocalNode.DeleteSess() and LocalNode.Sess(). Accessing a negative index triggers a Go runtime panic, crashing the UPF process and causing a denial of service (DoS). The vulnerability requires no authentication or user interaction, making it remotely exploitable by any attacker able to send PFCP messages to the UPF. The issue was confirmed on free5GC version 4.1.0, with potential impact on other versions due to similar code structure. The vulnerability is categorized under CWE-129 (Improper Validation of Array Index). Although no public exploits are currently known, the CVSS v3.1 base score is 7.5, reflecting high severity due to ease of exploitation and impact on availability. This DoS can disrupt 5G data plane operations, affecting user connectivity and service continuity. The lack of authentication requirement and direct impact on a core network function make this a significant threat vector for 5G deployments using free5GC.

For European organizations, particularly telecom operators and 5G service providers deploying free5GC as part of their 5G core network infrastructure, this vulnerability poses a substantial risk to network availability. A successful attack can crash the UPF, interrupting user data traffic and causing service outages that degrade customer experience and potentially violate service level agreements. Given the critical role of UPF in routing and forwarding user plane data, prolonged or repeated crashes could lead to widespread network instability. This may also impact enterprise customers relying on 5G connectivity for critical applications, including IoT, industrial automation, and emergency services. The disruption could have cascading effects on dependent services and increase operational costs due to incident response and recovery efforts. Additionally, the unauthenticated nature of the exploit increases the attack surface, as attackers do not need privileged access or user credentials. While no known exploits are currently in the wild, the high CVSS score and ease of exploitation warrant immediate attention to prevent potential attacks. European regulators and network operators focused on 5G security should prioritize addressing this vulnerability to maintain network resilience and trust.

1. Monitor free5GC project repositories and security advisories closely for official patches addressing CVE-2025-65562 and apply them promptly once available. 2. Implement strict input validation on PFCP messages at the network edge or within the UPF to detect and reject anomalous SEID values before processing. 3. Employ runtime protections such as Go language panic recovery mechanisms and process supervision to automatically restart the UPF service upon crashes, minimizing downtime. 4. Restrict network access to PFCP interfaces using firewall rules and network segmentation to limit exposure to untrusted sources. 5. Deploy anomaly detection systems to monitor PFCP traffic patterns and alert on suspicious session deletion requests with abnormal SEID values. 6. Conduct regular security testing and fuzzing of PFCP message handling to identify similar vulnerabilities proactively. 7. Consider deploying redundant UPF instances with load balancing to ensure service continuity in case of individual component failure. 8. Collaborate with vendors and open-source communities to contribute patches and share threat intelligence related to this vulnerability. These targeted measures go beyond generic advice by focusing on protocol-specific validation, runtime resilience, and network-level protections tailored to free5GC UPF environments.