Open5GS SMF DoS Flaws CVE-2026-8251, CVE-2026-8249 Exploited Publicly

Executive Summary

Two denial-of-service vulnerabilities in the Open5GS 5G core network software, tracked as CVE-2026-8251 and CVE-2026-8249, allow remote attackers to crash the Session Management Function (SMF) component. Both flaws carry a CVSS score of 4.3 and affect Open5GS up to version 2.7.7. Public exploit code has been published, and the project maintainers were notified via an issue report but have not yet released a fix, according to NVD entries published on May 10, 2026. Mobile network operators and researchers running Open5GS testbeds or production deployments should treat these as an immediate operational risk.

Technical Analysis

Both vulnerabilities reside in the same code path: the function update_authorized_pcc_rule_and_qos in the file /src/smf/npcf-handler.c. This function is part of the SMF component, which handles session management and policy control in 5G core networks. The SMF communicates with the Policy Control Function (PCF) to receive authorized Policy and Charging Control (PCC) rules and quality-of-service (QoS) parameters.

According to the NVD descriptions, a remote attacker can trigger a denial-of-service condition by sending a crafted request that manipulates the PCC rule and QoS update process. The exact mechanism is not detailed in the public advisories, but the function likely fails to properly validate input or handle error conditions when processing malformed policy updates, leading to a crash or hang of the SMF process.

CVE-2026-8251 and CVE-2026-8249 are nearly identical in scope and impact. The NVD entries differ only in their CVE identifiers and minor phrasing, suggesting they may represent two distinct attack vectors within the same function, or that the same underlying issue was assigned two CVE IDs during disclosure. Both are remotely exploitable and require no authentication, per the CVSS vector. The attack complexity is low, and no user interaction is required.

The fact that exploit code has been made public significantly raises the risk profile. While the CVSS base score of 4.3 is classified as "medium," the availability of working exploits in open-source intelligence channels means that even low-skill attackers can crash an SMF instance. In a production 5G core, an SMF outage would disrupt session management for all connected User Equipment (UE), effectively taking down data connectivity for subscribers served by that SMF.

Open5GS is an open-source implementation of the 3GPP-defined 5G Core (5GC) and Evolved Packet Core (EPC) network functions. It is widely used for research, development, and testing by telecom vendors, operators, and academic institutions. Some smaller operators and private 5G deployments may also run Open5GS in production.

Mitigations & Recommendations

As of May 11, 2026, the Open5GS project has not released a patched version. The NVD entries note that the project was "informed of the problem early through an issue report but has not responded." Defenders should monitor the Open5GS GitHub repository for a fix and apply it immediately upon release.

In the interim, network operators should consider the following mitigations:

• Restrict SMF network exposure: Ensure the SMF's N7 interface (toward the PCF) and any other management interfaces are not reachable from untrusted networks. Use firewall rules to limit access to only authorized PCF instances.
• Deploy network-based intrusion detection: Monitor for anomalous PCC rule update messages that may indicate exploitation attempts. The specific patterns are not yet publicly documented, but defenders can baseline normal SMF traffic and alert on deviations.
• Isolate Open5GS instances: If possible, run the SMF in a container or virtual machine with resource limits to contain the impact of a crash. Use orchestration tools to automatically restart a failed SMF.
• Consider downgrading or feature-gating: If the update_authorized_pcc_rule_and_qos functionality is not critical in a given deployment, operators may choose to disable or stub out the function until a patch is available. This should be tested thoroughly in a lab environment first.
• Engage the community: Open5GS is a community-driven project. Affected users should upvote or comment on the existing issue report to signal urgency and potentially accelerate a fix.

For test and research environments, the risk is lower but non-zero. Ensure that Open5GS instances are not exposed to the public internet and are segmented from production networks.