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AUSCERT Security Bulletin
Increased levels of SSH scanning
2 October 2009
AusCERT Security Bulletin Summary
Operating System: Windows
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Unauthorised Access -- Remote/Unauthenticated
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. 
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.
 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
Internet Email: email@example.com
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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