full-disclosure - Re: targetted SSH bruteforce attacks

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Message-ID: <BLU148-W8796A387DA5117D4D3A9EB4DF0@phx.gbl>
Date: Thu, 17 Jun 2010 15:58:33 -0500
From: John Jacobs <flamdugen@...mail.com>
To: <pschmehl_lists@...rr.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: targetted SSH bruteforce attacks

> > Of course it's wise to disable password authentication and just use
> > public key authentication.
> 
> Why?  Ssh is encrypted, so you're not exposing a password when you login.  How 
> does public key authentication make you more secure (in a practical sense)?
> 

Paul, it's more secure in that brute force attacks are mitigated because the private key is required by the client and the public key must appear in ~/.ssh/authorized_keys.  Disabling password authentication means a weak password on an account cannot be compromised by brute force or other discovery efforts.  A password on the private key provides even greater defense-in-depth security.

Disable password authentication and enforce key-pair authentication and targeted brute-force attacking becomes moot very quickly.  Moving SSHd from TCP 22 also keeps the script-kiddies and automated scanners away.

After doing these two basic things then it's time to focus on fail2ban, denyhosts, and the other firewall integrating solutions.

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