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                         AUSCERT Security Bulletin

                               ASB-2009.1072
         Asterisk releases updated versions to correct a resource
                         exhaustion vulnerability
                             4 September 2009

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

Product:              Asterisk Open Source
                      Asterisk Business Edition
                      S800i (Asterisk Appliance)
Operating System:     UNIX variants (UNIX, Linux, OSX)
Impact/Access:        Denial of Service -- Remote/Unauthenticated
Resolution:           Patch/Upgrade
CVE Names:            CVE-2009-2346  
Member content until: Sunday, October  4 2009

OVERVIEW

        A vulnerability has been corrected in Asterisk relating to IAX2 Call 
        Number Resource Exhaustion.


IMPACT

        The vendor has provided the following information regarding this
        vulnerability:
        
        "The IAX2 protocol uses a call number to associate messages with the 
        call that they belong to. However, the protocol defines the call 
        number field in messages as a fixed size 15 bit field. So, if all 
        call numbers are in use, no additional sessions can be handled.
        A call number gets created at the start of an IAX2 message exchange. 
        So, an attacker can send a large number of messages and consume the 
        call number space. The attack is also possible using spoofed source 
        IP addresses as no handshake is required before a call number is 
        assigned." [1]


MITIGATION

        The following versions of Asterisk correct this vulnerability [1]:
        
        Asterisk Open Source		1.2.35
        Asterisk Open Source		1.4.26.2
        Asterisk Open Source		1.6.0.15
        Asterisk Open Source		1.6.1.6
        Asterisk Business Edition	B.2.5.10
        Asterisk Business Edition	C.2.4.3
        Asterisk Business Edition	C.3.1.1
        S800i (Asterisk Appliance)	1.3.0.3
        
        Download locations for these versions are listed in the vendor's
        advisory. [1]


REFERENCES

        [1] Asterisk Project Security Advisory - AST-2009-006
            http://downloads.asterisk.org/pub/security/AST-2009-006.html

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

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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)
                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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