schpw.c in the kpasswd service in kadmind in MIT Kerberos 5 (aka krb5) before 1.11.3 does not properly validate UDP packets before sending responses, which allows remote attackers to cause a denial of service (CPU and bandwidth consumption) via a forged packet that triggers a communication loop, as demonstrated by krb_pingpong.nasl, a related issue to CVE-1999-0103.