Protecting SSH from brute force attacks

[Chris]

Daniel Bye wrote:
> On Fri, 8 October, 2004 8:44 am, spam maps said:
> 
>>Vulpes Velox wrote:
>>
>>>On Thu, 7 Oct 2004 15:15:25 -0700 (PDT) Luke <luked at pobox.com> wrote:
>>>
>>>
>>>>There are several script kiddies out there hitting my SSH server
>>>>every day.  Sometimes they attempt to brute-force their way in
>>>
>>>man login.conf for more info :)
>>
>>I'm just guessing, but are you trying to tell me that "login-retries" in
>>login.conf is useful?
>>
>>I have tried that by setting it to 2, but it seems to have no effect on
>>the sshd login behaviour. I always can try the password 6 times:
>>
>>$ ssh myname at my.own.pc
>>Password:
>>Password:
>>Password:
>>myname at my.own.pc's password:
>>Permission denied, please try again.
>>myname at my.own.pc's password:
>>Permission denied, please try again.
>>myname at my.own.pc's password:
>>Permission denied (publickey,password,keyboard-interactive).
>>$
>>
>>So could you be a little more specific as to where login.conf is of help
>>here?
> 
> 
> This is still only one *connection* - sshd will offer you (or anyone else
> who can connect) a certain number of chances to prove your identity. 
> Login.conf can't help with this.  You can configure sshd to stop offering
> the keyboard-interactive auth method - set
> 
> ChallengeResponseAuthentication no
> 
> in /etc/ssh/sshd_config and HUP the daemon.  You will no longer see the
> first three Password: prompts.
> 
> Login.conf can help you to limit the number of successive login attempts. 
> Make sure you run "cap_mkdb /etc/login.conf" whenever you edit the file,
> or you will not enable your changes.
> 
> Dan
> 


In addition, if you use ipfw, do something like this:

# Allow in SFTP, SSH, and SCP from public Internet
${fwcmd} add 090 pass log tcp from xxx.xxx.xxx.xxx/xx to ${ip} 22 setup 
limit src-addr 4

This simply allows ssh access to a certain subnet etc. In addition, the 
limit src-addr 4 allows only 4 connects etc.


-- 
Best regards,
Chris

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