CVE-2011-4539: DHCP Regular Expressions Segfault


DHCP Regular Expressions Segfault

Segmentation fault from dhcpd while processing an evaluated regular expression

Document Version:1.2

Posting date: 07 Dec 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




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:

  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.

Active exploits: None known at this time.

Solution: Upgrade to 4.1-ESV-R4 or 4.2.3-P1

Download patched versions from the following location:

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