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             AUSCERT External Security Bulletin Redistribution

                          DHCP: Denial of service
                              9 December 2011


        AusCERT Security Bulletin Summary

Product:           DHCP
Publisher:         ISC
Operating System:  UNIX variants (UNIX, Linux, OSX)
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2011-4539  

Original Bulletin: 

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Security Advisory - DHCP Regular Expressions Segfault

   Segmentation fault from dhcpd while processing an evaluated regular
   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
   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.

   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
   Related Document:


   - 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:

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