CVE-2013-2266: A Maliciously Crafted Regular Expression Can Cause Memory Exhaustion in named
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CVE-2013-2266: A Maliciously Crafted Regular Expression Can Cause Memory Exhaustion in named

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Article summary

A critical defect in BIND 9 allows an attacker to cause excessive memory consumption in named or other programs linked to libdns.

CVE: CVE-2013-2266

Document version: 2.0

Posting date: 26 March 2013

Program impacted: BIND

Versions affected: "Unix" versions of  BIND 9.7.x, 9.8.0 -> 9.8.5b1, 9.9.0 -> 9.9.3b1. (Windows versions are not affected. Versions of BIND 9 prior to BIND 9.7.0 (including BIND 9.6-ESV) are not affected. BIND 10 is not affected.)

Severity: Critical

Exploitable: Remotely


A flaw in a library used by BIND 9.7, 9.8, and 9.9, when compiled on Unix and related operating systems, allows an attacker to deliberately cause excessive memory consumption by the named process, potentially resulting in exhaustion of memory resources on the affected server. This condition can crash BIND 9 and will likely severely affect operation of other programs running on the same machine.

Please note: Versions of BIND 9.7 are beyond their "end of life" (EOL) and no longer receive testing or security fixes from ISC. However, the re-compilation method described in the "Workarounds" section of this document will prevent exploitation in BIND 9.7 as well as in currently supported versions.

Additional information is available in the CVE-2013-2266 FAQ and Supplemental Information article in the ISC Knowledgebase,


Intentional exploitation of this condition can cause denial of service in all authoritative and recursive nameservers running affected versions of BIND 9 [all versions of BIND 9.7, BIND 9.8.0 through 9.8.5b1 (inclusive) and BIND 9.9.0 through BIND 9.9.3b1 (inclusive)]. Additionally, other services which run on the same physical machine as an affected BIND server could be compromised through exhaustion of system memory.

Programs using the libdns library from affected versions of BIND are also potentially vulnerable to exploitation of this bug if they can be forced to accept input which triggers the condition. Tools which are linked against libdns (e.g. dig) should also be rebuilt or upgraded, even if named is not being used.

CVSS Score: 7.8

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

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


Patched versions are available (see the "Solutions:" section below) or operators can prevent exploitation of this bug in any affected version of BIND 9 by compiling without regular expression support.

Compilation without regular expression support:

BIND 9.7 (all versions), BIND 9.8 (9.8.0 through 9.8.5b1), and BIND 9.9 (9.9.0 through 9.9.3b1) can be rendered completely safe from this bug by re-compiling the source with regular expression support disabled. In order to disable inclusion of regular expression support:

  • After configuring BIND features as desired using the configure script in the top level source directory, manually edit the "config.h" header file that was produced by the configure script.
  • Locate the line that reads "#define HAVE_REGEX_H 1" and replace the contents of that line with "#undef HAVE_REGEX_H".
  • Run "make clean" to remove any previously compiled object files from the BIND 9 source directory, then proceed to make and install BIND normally.

Active exploits: No known active exploits.


Compile BIND 9 without regular expression support as described in the "Workarounds" section of this advisory, or upgrade to the patched release most closely related to your current version of BIND. These can be downloaded from

  • BIND 9 version 9.8.4-P2
  • BIND 9 version 9.9.2-P2

Acknowledgements: ISC would like to thank Matthew Horsfall of Dyn, Inc. for discovering this bug and bringing it to our attention.

Document Revision History:

1.0 Phase One - Advance Notification, 11 March 2013
1.1 Phase Two & Three, 25 March 2013
2.0 Notification to Public (Phase Four), 26 March 2013

Related Documents:

Japanese Translation:
Spanish Translation:
German Translation:
Portuguese Translation:

If you'd like more information on ISC Subscription Support and Advance Security Notifications, please visit

See our BIND 9 Security Vulnerability Matrix for a complete listing of security vulnerabilities and versions affected.

Do you still have questions? Questions regarding this advisory should go to security-officer@isc.orgTo report a new issue, please encrypt your message using's PGP key which can be found here: If you are unable to use encrypted email, you may also report new issues at:

Note: ISC patches only currently supported versions. When possible, we indicate EOL versions affected. (For current information on which versions are actively supported, please see

ISC Security Vulnerability Disclosure Policy: Details of our current security advisory policy and practice can be found in the ISC Software Defect and Security Vulnerability Disclosure Policy.

This Knowledgebase article is the complete and official security advisory document.

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