Knowledge Base ISC Main Website Ask a Question/Contact ISC
CVE-2012-3868: High TCP Query Load Can Trigger a Memory Leak in BIND 9
Author: Michael McNally Reference Number: AA-00730 Views: 21876 Created: 2012-07-20 17:02 Last Updated: 2012-07-30 18:25 0 Rating/ Voters

Title: High TCP Query Load Can Trigger a Memory Leak in BIND 9


Under heavy incoming TCP query loads named experiences a memory leak which may lead to significant reductions in query response performance. Additionally, this can trigger an automatic shutdown if named is running on a system that kills out-of-memory processes.

CVE: CVE-2012-3868

Document Version: 2.1

Posting date: 24 July 2012

Program Impacted: BIND9

Versions affected: 9.9.0 through 9.9.1-P1

Severity: High

Exploitable: Remotely


BIND 9 tracks incoming queries using a structure called "ns_client". When a query has been answered and the ns_client structure is no longer needed, it is stored on a queue of inactive ns_clients. When a new ns_client is needed to service a new query, the queue is checked to see if any inactive ns_clients are available before a new one is allocated; this speeds up the system by avoiding unnecessary memory allocations and de-allocations. However, when the queue is empty, and one thread inserts an ns_client into it while another thread attempts to remove it, a race bug could cause the ns_client to be lost; since the queue would appear empty in that case, a new ns_client would be allocated from memory. This condition occurred very infrequently with UDP queries but much more frequently under high TCP query loads; over time, the number of allocated but misplaced ns_client objects could grow large enough to affect system performance, and could trigger an automatic shutdown of the named process on systems with an "OOM killer" (out of memory killer) mechanism.

CVSS Score: 5.0

CVSS Equation: (AV:N/AC:L/Au:N/C:N/I:N/A:P)

For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit:

Workarounds: None available

Solution: Upgrade to BIND 9 version 9.9.1-P2.

BIND 9.9.1-P2 is available from

Exploit Status: Not known

Acknowledgment: ISC would like to thank Kevin Sheehan of Infoblox, Inc., and Anand Buddhdev from the RIPE NCC.

Document Revision History:

1.0 -Phase 1 contacted 11 July, 2012 
1.1 -Phase 1 re-issued 17 July, 2012. Re-released this patch with additional code to Phase 1.

1.2 - 23 July 2012 Phase 2 & 3 notified
2.0 - 24 July 2012 Phase 4-Public released

2.1 - 30 July 2012 Added Chinese Translation


Legal Disclaimer:

Internet Systems Consortium (ISC) is providing this notice on an "AS IS" basis. No warranty or guarantee of any kind is expressed in this notice and none should be inferred. ISC expressly excludes and disclaims any warranties regarding this notice or materials referred to in this notice, including, without limitation, any inferred warranty of merchantability, fitness for a particular purpose, absence of hidden defects, or of non-infringement. Your use of, or reliance on, this notice or materials referred to in this notice is at your own risk. ISC may change this notice at any time.

A stand-alone copy or paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy. Uncontrolled copies may lack important information, be out of date, or contain factual errors.

© 2001-2018 Internet Systems Consortium

For assistance with problems and questions for which you have not been able to find an answer in our Knowledge Base, we recommend searching our community mailing list archives and/or posting your question there (you will need to register there first for your posts to be accepted). The bind-users and the dhcp-users lists particularly have a long-standing and active membership.

ISC relies on the financial support of the community to fund the development of its open source software products. If you would like to support future product evolution and maintenance as well having peace of mind knowing that our team of experts are poised to provide you with individual technical assistance whenever you call upon them, then please consider our Professional Subscription Support services - details can be found on our main website.

  • There is no feedback for this article
Quick Jump Menu