The kdbldap plugin in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.9 through 1.9.1, when the LDAP back end is used, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a kinit operation with incorrect string case for the realm, related to the isprincipalinrealm, krb5seterrormessage, krb5ldapgetprincipal, and processasreq functions.