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                         AUSCERT Security Bulletin

                               ASB-2009.1033
        BIND 9 update for critical Denial of Service vulnerability
                               29 July 2009

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:              BIND 9
Operating System:     UNIX variants (UNIX, Linux, OSX)
                      Windows
                      Network Appliance
Impact/Access:        Denial of Service -- Remote/Unauthenticated
Resolution:           Patch
CVE Names:            CVE-2009-0696  
Member content until: Friday, August 28 2009

OVERVIEW

        ISC has released updated versions of BIND 9 to solve a remotely
        exploitable Denial of Service vulnerability for which exploit code
        is publicly available. [1]
        
        This vulnerability can be exploited by sending a specially crafted
        dynamic update message to a zone for which the BIND server is master.
        BIND servers that are master for one or more zones don't need to be
        configured to allow dynamic updates for this exploit to be effective.
        Therefore access controls cannot be used as a workaround.


IMPACT

        Exploitation of this vulnerability causes the BIND service to crash. [1]


MITIGATION

        Upgrade BIND to either 9.4.3-P3, 9.5.1-P3 or 9.6.1-P1. These versions
        can be downloaded from:
        
        http://ftp.isc.org/isc/bind9/9.6.1-P1/bind-9.6.1-P1.tar.gz
        http://ftp.isc.org/isc/bind9/9.5.1-P3/bind-9.5.1-P3.tar.gz
        http://ftp.isc.org/isc/bind9/9.4.3-P3/bind-9.4.3-P3.tar.gz
        
        A possible workaround is to block the traffic which exploits the
        vulnerability by implementing the following iptables rule:
        
         	iptables -A INPUT -p udp --dport 53 -j DROP -m u32 --u32
        	 '30 >> 27 & 0x0F = 5'
        
        AusCERT has not tested the workaround mentioned above.


REFERENCES

        [1] BIND Dynamic Update DoS
            https://www.isc.org/node/474

        [2] ISC BIND 9 vulnerable to denial of service via dynamic update
            request
            http://www.kb.cert.org/vuls/id/725188

AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

===========================================================================
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)
                AusCERT personnel answer during Queensland business hours 
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
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