CVE-2026-44321

free5GC's SMF UPI POST /upi/v1/upNodesLinks exits the SMF process on overlapping UE pools (unauthenticated, reachable Fatalf)

Unauthenticated process-kill DoS on the SMF management plane.

1. Missing inbound authentication (CWE-306) and authorization (CWE-862) on the UPI route group makes the trigger reachable to any off-path network attacker who can reach SMF on the SBI -- no token, no UE state needed. The same-instance nsmf-oam returning 401 (see free5gc/free5gc#887) proves OAuth middleware is wired in for other SMF route groups and only missing on UPI.
2. Reachable assertion / fail-fast (CWE-617): topology parsing calls logger.InitLog.Fatalf(...) on attacker-influenced validation failures. Fatalf is os.Exit(1)-equivalent -- it skips Gin's recovery, the deferred handlers, and kills the whole SMF process. This is materially worse than the related panic-DoS in free5gc/free5gc#905, which Gin recovers from at the goroutine level.

Any party that can reach SMF on the SBI can:

• Send one unauthenticated POST with an overlapping UE pool and immediately terminate the SMF process, dropping all of SMF's SBI surface (PDU-session establishment, UE policy interactions) until SMF is restarted.
• Repeat the trigger after every restart to sustain the outage.
• Use sibling Fatalf paths (invalid-pool, static-pool exclusion) to sustain the same DoS even if the overlap check is hardened in isolation, because the underlying defect is using Fatalf for request-time validation on an unauthenticated handler.

No Confidentiality impact (the crash returns no data to the attacker). No persistent Integrity impact (the topology updates are in-memory and are lost when SMF dies). The whole impact concentrates in Availability: complete loss of SMF service via a single unauthenticated request.

Affected: free5gc v4.2.1.

Upstream issue: https://github.com/free5gc/free5gc/issues/906
Upstream fix: https://github.com/free5gc/smf/pull/203

A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.

CVE-2026-44321 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-44321? CVE-2026-44321 is a high-severity missing authentication for critical function vulnerability in github.com/free5gc/smf (go), affecting versions <= 1.4.3. No fixed version is listed yet. A critical operation is accessible without requiring any authentication.
2. How severe is CVE-2026-44321? CVE-2026-44321 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/free5gc/smf are affected by CVE-2026-44321? github.com/free5gc/smf (go) versions <= 1.4.3 is affected.
4. Is there a fix for CVE-2026-44321? No fixed version is listed for CVE-2026-44321 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-44321 exploitable, and should I be worried? Whether CVE-2026-44321 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44321 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44321? No fixed version is listed yet. In the interim: Keep the dependency up to date. Add authentication gating to all sensitive endpoints.