Once registered,
the attacker has full access to the same services as the legitimate subscriber.
If a hacker gains access to a subscriber??™s private user identity, the hacker will be
able to launch a REGISTER message from anyplace in the network. Remember that
a REGISTER identifies the subscriber??™s current location. Therefore, if the subscriber
is already registered, and the network receives a new registration, the network registrar
(the S-CSCF in IMS) will assume that the subscriber has changed locations, and
change the registration to the new location.
All new traffic will then be sent to the newly registered location. The legitimate subscriber
has no idea that his or her registration has been hijacked, and simply stops
receiving calls. If subscribers themselves change locations or power off their devices, the
registration will be changed again when they power their devices back up, and they will
restore control over their service. Of course by then the perpetrators have already gained
access to the services they were after, and have taken advantage of the free service.
140 Chapter 6
Server Impersonation
Server impersonation allows a proxy server in another network to ???pose??? or masquerade
as another legitimate proxy redirecting all traffic to itself and away from the legitimate
proxy. In the IMS domain, this would mean compromising the CSCF function
and redirecting requests and responses to the rogue CSCF.
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