CVE-2026-44327: free5GC: NEF nnef-oam route group is unauthenticated; no-token requests reach the OAM handler
Summary free5GC's NEF mounts the nnef-oam route group without inbound OAuth2/bearer-token authorization. A network attacker who can reach NEF on the SBI can hit the OAM route with no Authorization header at all and the handler returns 200 OK. The current OAM handler is a stub that returns null, but the structural defect is route-group-scoped: the entire OAM route group has no inbound auth middleware, so every future OAM operation added to this group inherits the missing auth boundary by default. Same root cause as the NEF traffic-influence and PFD-management findings.
Details Validated against the NEF container in the official Docker compose lab. - Source repo tag: v4.2.1 - Running Docker image: free5gc/nef:v4.2.0 - Runtime NEF commit: 5ce35eab - Docker validation date: 2026-03-11
NEF advertises OAuth2 setting receive from NRF: true, yet the OAM route group is mounted without any inbound auth middleware and answers unauthenticated GETs with 200 OK.
Code evidence (paths in free5gc/nef): - OAM route group mounted without auth middleware: NFs/nef/internal/sbi/server.go:60 - OAM route exposed at /: NFs/nef/internal/sbi/apioam.go:9 - OAM processor returns 200 OK directly: NFs/nef/internal/sbi/processor/oam.go:9 - NEF context only exposes outbound token acquisition (GetTokenCtx); there is no inbound authorization path: NFs/nef/internal/context/nefcontext.go:153
PoC Reproduced against the running NEF at http://10.100.200.19:8000 with no Authorization header:
curl -i http://10.100.200.19:8000/nnef-oam/v1/
Observed output: HTTP/1.1 200 OK null
NEF container logs (docker logs nef) show the request being served while OAuth is enabled: [INFO][NEF][GIN] | 200 | GET | /nnef-oam/v1/
Impact Missing inbound authentication (CWE-306) and authorization (CWE-862) on the NEF OAM SBI route group. Severity is scored against the OAM route group's intended capability surface (Operations / Administration / Maintenance), NOT against the current stub handler. The current handler is a stub that returns null, but the defect is route-group-scoped: there is no auth middleware on the group at all, so every future OAM operation added behind this group inherits the missing inbound auth boundary by default.
Any party that can reach NEF on the SBI can: - Probe and enumerate the OAM route surface anonymously today. - Hit any future OAM-group endpoint (read, modify, restart-style operations) anonymously, because the auth boundary does not exist for this group.
Operators who assume OAuth2 setting receive from NRF: true enforces inbound auth on NEF are wrong for this route group.
Affected: free5gc v4.2.1.
Upstream issue: https://github.com/free5gc/free5gc/issues/861 Upstream fix: https://github.com/free5gc/nef/pull/23
Other sources
free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's NEF mounts the nnef-oam route group without inbound OAuth2/bearer-token authorization. A network attacker who can reach NEF on the SBI can hit the OAM route with no Authorization header at all and the handler returns 200 OK. The current OAM handler is a stub that returns null, but the structural defect is route-group-scoped: the entire OAM route group has no inbound auth middleware, so every future OAM operation added to this group inherits the missing auth boundary by default. This vulnerability is fixed in 4.2.2.
— MITRE
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2026-44327?
The severity of CVE-2026-44327 is considered critical due to the potential for unauthorized access to the OAM route without any authorization.
How do I fix CVE-2026-44327?
To fix CVE-2026-44327, upgrade to version 1.2.4 or later of the affected free5GC NEF package.
What impact does CVE-2026-44327 have on my system?
CVE-2026-44327 allows attackers to access sensitive operational management routes without authentication, which could lead to exploitation or information leakage.
Is CVE-2026-44327 a remote vulnerability?
Yes, CVE-2026-44327 can be exploited remotely by attackers who can access the NEF on the Service-Based Interface (SBI).
What software versions are affected by CVE-2026-44327?
CVE-2026-44327 affects free5GC NEF versions up to and including 1.2.3.