The merge_authdata function in kdc_authdata.c in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.8.x before 1.8.4 does not properly manage an index into an authorization-data list, which allows remote attackers to cause a denial of service (daemon crash), or possibly obtain sensitive information, spoof authorization, or execute arbitrary code, via a TGS request that triggers an uninitialized pointer dereference, as demonstrated by a request from a Windows Active Directory client.