Free5GC PCF: Missing authentication middleware in Npcf_SMPolicyControl allows access to SM policy handlers and disclosure of subscriber SUPI

Summary

PCF Npcf_SMPolicyControl missing authentication middleware allows unauthenticated access to SM policy handlers and disclosure of subscriber SUPI

Details

In NewServer(), the smPolicyGroup route group is created and routes are applied without attaching the router authorization middleware. In contrast, other PCF service groups such as Npcf_PolicyAuthorization do attach RouterAuthorizationCheck before route registration.

Because the middleware is missing, requests to the following endpoints can reach business logic even when no valid OAuth token is provided:

• POST /npcf-smpolicycontrol/v1/sm-policies
• GET /npcf-smpolicycontrol/v1/sm-policies/{smPolicyId}
• POST /npcf-smpolicycontrol/v1/sm-policies/{smPolicyId}/update
• POST /npcf-smpolicycontrol/v1/sm-policies/{smPolicyId}/delete

This is visible at runtime because unauthenticated requests return business-level responses such as 400 or 404 instead of being rejected with 401 before handler execution. Under valid lab preconditions (existing UE/session context and related policy data), unauthenticated POST /sm-policies can succeed with 201, and unauthenticated GET /sm-policies/{id} can succeed with 200 and return policy context containing subscriber identifiers including supi.

The root cause is missing router auth enforcement for Npcf_SMPolicyControl. Upstream also fixed this by adding RouterAuthorizationCheck to smPolicyGroup (and uePolicyGroup) in free5gc/pcf PR #63.

PoC

1. Deploy free5GC with PCF reachable on the SBI network.
2. Use the PoC against the PCF service without an Authorization header:

   go run /home/ubuntu/free5gc/tools/npcf-smpolicy-noauth-poc/main.go \
     --pcf-root /home/ubuntu/free5gc/NFs/pcf \
     --pcf-url http://10.100.200.9:8000 \
     --timeout 4s
   

Observe that unauthenticated requests to Npcf_SMPolicyControl return business responses instead of 401.

Impact

This is an authentication/authorization bypass on a network-accessible SBI service. Any unauthenticated actor able to reach the PCF SBI interface can invoke Npcf_SMPolicyControl handlers directly.