There is a denial-of-service vulnerability in several versions of the Internet Software Consortium's (ISC) BIND software. This vulnerability is referred to by the ISC as the "zxfr bug." It affects ISC BIND version 8.2.2, patch levels 1 through 6.
Using this vulnerability, attackers on sites that are permitted to request zone transfers can force the name service daemon (named) running on vulnerable DNS servers to crash, disrupting name resolution service until the named daemon is restarted.
The preconditions for this attack to succeed are as follows:
The time between the attack and the crash of named may vary from system to system.
This vulnerability has been discussed in public forums. The ISC has confirmed that all platforms running version 8.2.2 of the BIND software prior to patch level 7 are vulnerable to this attack.
A remote attacker can use malicious zone transfers to crash vulnerable BIND servers, resulting in a denial-of-service condition that disables name resolution service.
Apply a patch from your vendor
If it is not possible to immediately upgrade systems affected by the "zxfr bug", the ISC recommends that users block zone transfers from untrusted hosts.
Compaq Computer Corporation
The CERT Coordination Center thanks Mark Andrews, David Conrad, and Paul Vixie of the ISC for developing a solution and assisting in the preparation of this document. We also thank Olaf Kirch for helping us to understand the exact nature of the "zxfr bug" vulnerability.