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AUSCERT External Security Bulletin Redistribution
DHCP: Denial of service
9 December 2011
AusCERT Security Bulletin Summary
Operating System: UNIX variants (UNIX, Linux, OSX)
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2011-4539
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Security Advisory - DHCP Regular Expressions Segfault
Segmentation fault from dhcpd while processing an evaluated regular
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.
None known at this time.
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
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