Vulnerability Note VU#715973

ISC BIND 8.2.2-P6 vulnerable to DoS via compressed zone transfer, aka the "zxfr bug"

Original Release date: 10 Nov 2000 | Last revised: 08 Aug 2001


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:

  • A compressed zone transfer (ZXFR) request must be made from a site allowed to make any zone transfer request (not just ZXFR).
  • A subsequent name service query of an authoritative and non-cached record must be made.

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

To address this vulnerability, the CERT/CC recommends that all users of ISC BIND upgrade to version 8.2.2-P7, which patches both VU#198355 and VU#715973. For information regarding vendor-specific versions of DNS software, please consult the Systems Affected section of this document.

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.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
CalderaAffected12 Nov 200016 May 2001
Compaq Computer CorporationAffected12 Nov 200016 May 2001
ConectivaAffected-16 May 2001
DebianAffected-16 May 2001
Hewlett PackardAffected12 Nov 200011 May 2001
IBMAffected12 Nov 200011 May 2001
ISCAffected-13 Nov 2000
MandrakeSoftAffected-13 Nov 2000
NetBSDAffected12 Nov 200013 Nov 2000
RedHatAffected12 Nov 200013 Nov 2000
SlackwareAffected-13 Nov 2000
SuSEAffected16 Nov 200011 May 2001
TrustixAffected16 Nov 200016 May 2001
FreeBSDNot Affected12 Nov 200011 May 2001
FujitsuNot Affected12 Nov 200011 May 2001
If you are a vendor and your product is affected, let us know.View More »

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



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.

This document was written by Jeffrey S. Havrilla and Jeffrey P. Lanza.

Other Information

  • CVE IDs: CVE-2000-0887
  • CERT Advisory: CA-2000-20
  • Date Public: 07 Nov 2000
  • Date First Published: 10 Nov 2000
  • Date Last Updated: 08 Aug 2001
  • Severity Metric: 33.08
  • Document Revision: 33


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