GitHub Security Advisory: GHSA-wqfh-gq79-j8mf
Package: github.com/free5gc/nef (GO)
Severity: HIGH (CVSS 7.3)
CWE: CWE-306: Missing Authentication for Critical Function, CWE-862: Missing Authorization
Vulnerable versions: <= 1.2.3
Patched in: unpatched

Summary: free5GC's NEF nnef-callback route group is unauthenticated; forged callback requests are accepted into the processing path

Details:
### Summary
free5GC's NEF mounts the `nnef-callback` route group without inbound OAuth2/bearer-token authorization. A forged or arbitrary bearer token (e.g. `Authorization: Bearer not-a-real-token`) is enough to reach the SMF-callback handler -- the callback body is parsed and dispatched into NEF business logic instead of being rejected at the auth boundary. Same root cause as the other NEF SBI findings: the route group is mounted without any inbound auth middleware. NEF does not authenticate the producer NF identity before processing callback content; if an attacker can guess or obtain a valid `NotifId`, this missing auth boundary lets forged callbacks act on real subscription state. The route group is also reachable even when the runtime `ServiceList` does not declare it (it lists only `nnef-pfdmanagement` and `nnef-oam`).

### Details
Validated against the NEF container in the official Docker compose lab.
- Running Docker image: `free5gc/nef:v4.2.1`
- Docker validation date: 2026-03-11

NEF advertises `OAuth2 setting receive from NRF: true`, yet the `nnef-callback` route group is mounted with no inbound auth middleware. The API layer reads the raw request body and deserializes it before any auth check, then the processor looks up subscription state by `NotifId`.

Code evidence (paths in `free5gc/nef`):
- Callback route group mounted without auth middleware: `NFs/nef/internal/sbi/server.go:64`
- Callback route exposed at `/notification/smf`: `NFs/nef/internal/sbi/api_callback.go:13`
- API layer reads raw request bytes and deserializes them before any auth check: `NFs/nef/internal/sbi/api_callback.go:23`
- Processor looks up the subscription by `NotifId`: `NFs/nef/internal/sbi/processor/callback.go:13`
- NEF context only exposes outbound token acquisition (`GetTokenCtx`); there is no inbound authorization path: `NFs/nef/internal/context/nef_context.go:153`
- Config validation only allows `nnef-pfdmanagement` and `nnef-oam`: `NFs/nef/pkg/factory/config.go:126`

### PoC
Reproduced against the running NEF at `http://10.100.200.19:8000` using a fabricated bearer token.

Send a forged callback request:
```
curl -i \
  -H 'Authorization: Bearer not-a-real-token' \
  -H 'Content-Type: application/json' \
  --data '{"notifId":"forged-notif","eventNotifs":[]}' \
  http://10.100.200.19:8000/nnef-callback/v1/notification/smf
```

Observed output:
```
HTTP/1.1 404 Not Found
{"title":"Data not found","status":404,"detail":"Subscription is not found"}
```

The `404` is positive auth-bypass evidence: the request was parsed and dispatched into the callback business handler instead of being rejected at the auth boundary. NEF container logs (`docker logs nef`) confirm the callback handler was reached:
```
[INFO][NEF][TraffInfl] SmfNotification - NotifId[forged-notif]
[INFO][NEF][GIN] | 404 | POST | /nnef-callback/v1/notification/smf
```

### Impact
Missing inbound authentication (CWE-306) and authorization (CWE-862) on the NEF `nnef-callback` SBI route group. Thi