krb5: PKINIT null pointer deref leads to DoS

The pkinitserverreturnpadata function in plugins/preauth/pkinit/pkinitsrv.c in the PKINIT implementation in the Key Distribution Center KDC in MIT Kerberos 5 aka krb5 before 1.10.4 attempts to find an agility KDF identifier in inappropriate circumstances, which allows remote attackers to cause a...