Assume: the attacker has legitimate insider access to a Kerberos system.
Background: The attacker is looking to invalidate all tickets for a service (maybe he really dislikes a service). To do so, he wants to exploit his access to the system in order to mess with the NTP protocol.
Question: How could the user invalidate all of the tickets for the service he does not like?
As the ticket granting server is doing the polling to establish the correct time via the NTP protocol, I don't see how a malicious attacker could invalidate the tickets for a specific service by messing with the timing. Is this possible?