This indicates an attack attempt to exploit a Denial of Service vulnerability in MIT Kerberos.
The vulnerability is due to a NULL pointer dereference error when vulnerable module handles a maliciously crafted packet. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system via a maliciously crafted packet.
MIT Kerberos krb5-1.13.1 and prior
Denial of Service: Remote attackers can crash vulnerable systems or services
Apply the most recent upgrade or patch from the vendor.