CVE-2026-1684 is a denial of service (DoS) vulnerability identified in the Free5GC Session Management Function (SMF) component, specifically affecting versions 4.0 and 4.1.0. The vulnerability resides in the HandleReports function of the PFCP UDP Endpoint, implemented in the /internal/context/pfcp_reports.go file. PFCP (Packet Forwarding Control Protocol) is a critical protocol used between the SMF and User Plane Function (UPF) in 5G core networks to manage session and forwarding rules. The vulnerability allows an attacker to send specially crafted PFCP reports to the SMF, causing it to malfunction and resulting in denial of service. This attack can be executed remotely over the network without requiring any authentication or user interaction, increasing its risk profile. The vulnerability does not impact confidentiality or integrity but affects availability by disrupting the SMF’s ability to process PFCP reports correctly. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X) indicates network attack vector, low attack complexity, no privileges or user interaction needed, and low impact on availability. No known exploits have been reported in the wild to date. Free5GC is an open-source 5G core network implementation widely used for research, development, and some production environments, making this vulnerability relevant to organizations deploying or testing 5G core networks with Free5GC SMF. The absence of a patch link suggests that remediation may require applying updates once available or implementing temporary network-level protections.

The primary impact of CVE-2026-1684 is the disruption of the 5G core network’s Session Management Function, which is responsible for session establishment, modification, and release. A successful denial of service attack can degrade or halt 5G service availability, affecting end-user connectivity and potentially causing cascading failures in dependent network functions. For telecommunications providers and enterprises relying on Free5GC SMF, this can lead to service outages, customer dissatisfaction, and financial losses. Given the critical role of 5G networks in supporting IoT, critical infrastructure, and enterprise applications, prolonged or widespread DoS could have broader economic and operational consequences. Although no confidentiality or integrity impact is noted, availability degradation in core network components is a significant risk. The remote and unauthenticated nature of the exploit increases the threat surface, especially in environments where the SMF PFCP endpoint is exposed or insufficiently protected. However, the lack of known exploits in the wild and the medium severity rating suggest the threat is moderate but warrants timely mitigation.

Organizations should monitor Free5GC project updates and apply security patches promptly once available to address CVE-2026-1684. In the interim, network administrators should restrict access to the PFCP UDP endpoint of the SMF by implementing strict firewall rules and network segmentation to limit exposure to untrusted networks. Deploying intrusion detection or prevention systems (IDS/IPS) with signatures or heuristics to detect anomalous PFCP traffic patterns can help identify and block exploitation attempts. Additionally, logging and monitoring PFCP traffic for unusual report patterns can provide early warning of attack attempts. Network operators should also consider rate limiting PFCP messages to reduce the risk of DoS from flooding attacks. Conducting regular security assessments and penetration testing on 5G core components can help identify similar vulnerabilities proactively. Finally, organizations should maintain an incident response plan tailored to 5G core network disruptions to minimize downtime and service impact.