Re: a GOOD idea to harden OpenSSH!

you can already use fail2ban to accomplish this kind of thing.

the original idea i think is somewhat terrible in a multi-user 
enterprise-y kind of environment since you'll wind up telling users that 
they have to wait 2 seconds before entering their passphrase 
constantly.  for your home server it might work, but you can always 
setup public keys or OTP pretty easily as well, in addition to fail2ban.

you can also use pam_tally to only allow 6 failed passwords in a row 
before locking the account.  i run the cronjob to unlock all the 
accounts every 30 mins or so, which only allows a velocity of 12 guess 
per hour on a single account, while not requiring users with locked 
accounts to call up a helpdesk.



On 3/31/11 11:24 AM, Joseph Spenner wrote:
> --- On Wed, 3/30/11, nagygabor88<[email protected]>  wrote:
>
>> From: nagygabor88<[email protected]>
>> Subject: a GOOD idea to harden OpenSSH!
>> To: "OpenSSH list"<[email protected]>
>> Date: Wednesday, March 30, 2011, 12:19 PM
>>
>>
>> if a user wants to connect to an ssh server then he have to
>> wait a couple of seconds, then he can write his passphare.
>> the "couple of seconds" is defined in the sshd config,
>> e.g.: 2 seconds
>> the method musn't show that the user have to wait 2 seconds
>> to write his passphare.
>>
> This can already be similarly done using iptables, with entries such as:
> $IPTABLES -N SSH_CHECK
> $IPTABLES -I INPUT -p tcp --dport 22 -m state --state NEW -j SSH_CHECK
> $IPTABLES -A SSH_CHECK -m recent --set --name SSH
> $IPTABLES -A SSH_CHECK -m recent --update --seconds 180 --hitcount 5 --rttl --name SSH -j LOG --log-prefix "SSH_brute_force "
> $IPTABLES -A SSH_CHECK -m recent --update --seconds 180 --hitcount 5 --rttl --name SSH -j DROP
>
> What this does:  If I get more than 5 hits within 180 seconds, block them for 180 seconds.
>
>