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                         AUSCERT Security Bulletin

                               ASB-2013.0016
               A vulnerability has been identified in GnuTLS
                              8 February 2013

===========================================================================

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

Product:              GnuTLS
Operating System:     Windows
                      UNIX variants (UNIX, Linux, OSX)
Impact/Access:        Access Privileged Data -- Remote with User Interaction
Resolution:           Patch/Upgrade
CVE Names:            CVE-2013-1619  
Member content until: Sunday, March 10 2013

OVERVIEW

        A vulnerability has been identified in GnuTLS prior to versions 3.1.7,
        3.0.28 and 2.12.23. [1] 


IMPACT

        The vendor has provided the following description regarding this
        vulnerability:
        
        "Nadhem Alfardan and Kenny Paterson devised an attack that recovers 
        some bits of the plaintext of a GnuTLS session that utilizes that CBC
        ciphersuites, by using timing information.
        
        In order for the attack to work the client must operate as follows. 
        It connects to a server, it sends some (encrypted) data that will be 
        intercepted by the attacker, who will terminate the client's 
        connection abnormally (i.e. the client will receive a premature 
        termination error). The client should repeat that, multiple times." [1]


MITIGATION

        The vendor has provided the following mitigations which includes 
        the application of a patch:
        
        "Do not enable the CBC ciphersuites, prefer ARCFOUR or GCM modes.
        Upgrade to the latest GnuTLS version (3.1.7, 3.0.28, or 2.12.23)." [1]


REFERENCES

        [1] TLS CBC padding timing attack
            http://www.gnutls.org/security.html#GNUTLS-SA-2013-1

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.

===========================================================================
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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