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                         AUSCERT Security Bulletin

                     Increased levels of SSH scanning
                              2 October 2009


        AusCERT Security Bulletin Summary

Product:              SSH
Operating System:     Windows
                      UNIX variants (UNIX, Linux, OSX)
                      Network Appliance
Impact/Access:        Unauthorised Access -- Remote/Unauthenticated
Resolution:           Mitigation
Member content until: Sunday, November  1 2009


        There has been an increase in ssh port scanning.


        Scanning on port 22 using the root username has been on the increase
        of late. This information has been confirmed by sans. [1]
        From privately received reports it appears attackers are using 
        botnets to brute force ssh accounts. Successful exploitation will
        result in unauthorised access. If root accounts are exploited the
        impacts would be much more severe, giving the attacker full system


        As brute forcing often attempt dictionary based passwords, you 
        should ensure a strong password policy is in place. By utilising
        botnets the attackers have the ability to process a large amount
        of connection attempts. When combined with password dictionary 
        attacks this can result in a greater chance of success. 
        Using techniques like rate limiting on ssh may help in mitigating 
        this style of attack. You should always ensure that root accounts 
        are not enabled via ssh. Administrators may also want to look into 
        using key based authentication to harden ssh security. Using a non
        standard port for ssh is often employed but this will not provide 
        a good level of security if the attack is targeted.


        [1] Increase in ssh root access attempts

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:


Australian Computer Emergency Response Team
The University of Queensland
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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