free5GC's NEF nnef-oam route group is unauthenticated; no-token requests reach the OAM handler
Date: 2026-05
Affected: go/github.com/free5gc/nef
Attack vector: auth-bypass
Category: vulnerability-disclosure
Severity: Critical
CVE: CVE-2026-44326
CVE-2026-44327
CWE: CWE-306
CWE-862
CVSS: 10 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:H)

### 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 `GET`s 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/api_oam.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/nef_context.go:153` ### PoC Reproduced against the running NEF at `http://10.100.200.19:8000


Mitigations:

Architectural layers (MAESTRO):