free5GC's PCF npcf-smpolicycontrol POST /sm-policies panics on downstream UDR/OpenAPI 404 via nil pointer dereference

Summary

free5GC's PCF POST /npcf-smpolicycontrol/v1/sm-policies handler (HandleCreateSmPolicyRequest) panics with a nil-pointer dereference when a downstream OpenAPI consumer call (UDR lookup) returns 404 Not Found and the consumer wrapper returns err != nil together with a nil response struct. The handler logs the OpenAPI error and continues executing instead of returning, then dereferences the nil response struct on a subsequent line and panics. Gin recovery converts the panic into HTTP 500, so a single attacker-shaped POST returns 500 instead of a clean 4xx whenever the downstream lookup fails. The PCF process keeps running.

The trigger is a single POST containing input that causes the downstream UDR lookup to fail (e.g. an unknown DNN). In v4.2.1 this endpoint is also reachable WITHOUT an Authorization header because the PCF Npcf_SMPolicyControl route group is mounted without inbound auth middleware (see free5gc/free5gc#844). So in the validation lab the trigger is fully unauthenticated.

Details

Validated against the PCF container in the official Docker compose lab.

• free5GC version: v4.1.0 (originally reported on v4.1.0; same defect present in v4.2.1)
• PCF endpoint: http://10.100.200.9:8000

Vulnerable handler path (paraphrased from the captured stack trace):

[INFO][PCF][SMpolicy] Handle CreateSmPolicy
[ERRO][PCF][Consumer] openapi error: 404, Not Found
[ERRO][PCF][GIN] panic: runtime error: invalid memory address or nil pointer dereference
  github.com/free5gc/pcf/internal/sbi/processor.(*Processor).HandleCreateSmPolicyRequest
      /go/src/free5gc/NFs/pcf/internal/sbi/processor/smpolicy.go:82 +0x562
  github.com/free5gc/pcf/internal/sbi.(*Server).HTTPCreateSMPolicy
      /go/src/free5gc/NFs/pcf/internal/sbi/api_smpolicy.go:86 +0x405

The handler's UDR-failure branch logs the OpenAPI error but does not return; the next line dereferences the nil response struct.

Code evidence (paths in free5gc/pcf):

• Panic site:
  • NFs/pcf/internal/sbi/processor/smpolicy.go:82
• Route dispatch:
  • NFs/pcf/internal/sbi/api_smpolicy.go:86

PoC

Reproduced end-to-end against the running PCF at http://10.100.200.9:8000.

Send a single POST whose dnn is unknown to UDR -- this drives the downstream OpenAPI call to return 404 Not Found, which then triggers the nil-deref panic: