GHSA-7g27-v5wj-jr75

free5GC UDM DataChangeNotification Procedure Panic Due to Nil Pointer Dereference

**Impact** This is a NULL Pointer Dereference vulnerability leading to Denial of Service. - **Security Impact**: A remote attacker can cause the UDM service to panic and crash by sending a crafted POST request to the `/sdm-subscriptions` endpoint with a malformed URL path containing path traversal sequences (`../`) and a large JSON payload. The `DataChangeNotificationProcedure` function in `notifier.go` attempts to access a nil pointer without proper validation, causing a complete service crash with "runtime error: invalid memory address or nil pointer dereference". - **Functional Impact**: The service crashes completely, requiring manual restart. All UDM functionality is disrupted until recovery. - **Affected Parties**: All deployments of free5GC v4.0.1 using the UDM HTTP callback functionality. **Patches** Yes, the issue has been patched. The fix is implemented in PR free5gc/udm#78. Users should upgrade to the next release of free5GC that includes this commit. **Workarounds** There is no direct workaround at the application level. The recommendation is to apply the provided patch or implement API gateway-level filtering to block requests containing path traversal sequences.