1. vSTP SS7 Security Guide
  2. Fraud
  3. Denial of Service

D.5 Denial of Service

Following are the types of attacks in a denial of service attack:

  • Service unavailability for subscriber
  • Recourses depletion

If the VLR address where the subscriber is currently registered is removed from the HLR via PurgeMS initiated by a certain third-party host, terminating calls cannot be routed to the subscriber's VLR/MSC. The reason is that there is no registration address in the HLR. In such a case, originating calls are available for the subscriber because the registration record in the VLR is not changed.

Rebooting the device does not help to restore the record in the HLR, because the VLR does not initiate the UpdateLocation procedure, assuming that there are no changes in the subscriber's registration data.

It is possible to restore the registration record and the subscriber's availability only by registering in the coverage area of another serving MSC. For example, first manually selecting the network of another operator and then selecting the home network again. Another method is to move to another MSC of the home network.