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AUSCERT External Security Bulletin Redistribution
ESB-2011.1227
DHCP: Denial of service
9 December 2011
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AusCERT Security Bulletin Summary
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Product: DHCP
Publisher: ISC
Operating System: UNIX variants (UNIX, Linux, OSX)
Windows
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2011-4539
Original Bulletin:
https://www.isc.org/software/dhcp/advisories/cve-2011-4539
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Security Advisory - DHCP Regular Expressions Segfault
Summary:
Segmentation fault from dhcpd while processing an evaluated regular
expression
CVE: CVE-2011-4539
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
Severity: Medium
Exploitable: remotely
Description:
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:
http://nvd.nist.gov/cvss.cfm?calculator&adv&version=2&vector=(tbd)
Workarounds:
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:
http://www.isc.org/software/dhcp
Acknowledgment:
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
Related Document:
References:
- Do you have Questions? Questions regarding this advisory should
go to security-officer@isc.org.
- ISC Security Vulnerability Disclosure Policy: Details of our
current security advisory policy and practice can be found here:
https://www.isc.org/security-vulnerability-disclosure-policy
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 implied. ISC expressly excludes and disclaims
any warranties regarding this notice or materials referred to in this
notice, including, without limitation, any implied warranty of
merchantability, fitness for a particular purpose, absence of hidden
defects, or of non-infringement. Your use 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 document URL is an uncontrolled copy. Uncontrolled copies may
lack important information, be out of date, or contain factual errors.
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Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
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On call after hours for member emergencies only.
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