Notice: ISC DHCP Security Advisory 7 Dec CVE-2011-4539

Susan Graves sgraves at
Wed Dec 7 20:46:32 UTC 2011

Title:  DHCP Regular Expressions Segfault

Summary: Segmentation fault from dhcpd while processing an evaluated
regular expression

CVE: CVE-2011-4539

Document Version: 1.2

Document url:

Posting date: 30 November 2011

Program Impacted: DHCP

Versions affected: 4.0.x and higher, including all EOL versions
                   back to 4.0, 4.1-ESV, and 4.2.x

Severity: Medium

Exploitable: Remotely

  A bug exists which allows an attacker who is able to send DHCP
  Request packets, either directly or through a relay, to remotely
  crash an ISC DHCP server if that server is configured to evaluate
  expressions using a regular expression (i.e. uses the "~=" or "~~"
  comparison operators.) Further details are being withheld to allow
  administrators of affected systems time to patch. You are potentially
  vulnerable if you use regular expression comparison operators in
  your dhcpd.conf

CVSS Score: 6.1

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:

  This bug cannot be triggered if you are not using regular expressions
  in your configuration file.

  Upgrade to 4.1-ESV-R4 or 4.2.3-P1
 Download patched versions from the following location:

Exploit Status: No known active exploits


  Thank you to BlueCat Networks for finding and testing the issue.

Document Revision History
1.0 30 November 2011 - Phase I notified
1.1 6 December 2011 - Phase II & III notified
1.2  7 December 2011 - Public Release

Document URL: to be posted with public release

- Do you have Questions? Questions regarding this advisory should
  go to security-officer at

- ISC Security Vulnerability Disclosure Policy: Details of our
  current security advisory policy and practice can be found here:

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