From owner-freebsd-security@FreeBSD.ORG  Sat Aug 19 21:29:41 2006
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Date: Sat, 19 Aug 2006 16:29:38 -0500
From: "Scot Hetzel" <swhetzel@gmail.com>
To: "Pieter de Boer" <pieter@thedarkside.nl>
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References: <44E76B21.8000409@thedarkside.nl>
Cc: freebsd-security@freebsd.org
Subject: Re: SSH scans vs connection ratelimiting
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On 8/19/06, Pieter de Boer <pieter@thedarkside.nl> wrote:
> This works as expected, IP-addresses are added to the 'lamers'-table
> every once in a while.
>
> However, there apparently are SSH bruteforcers that simply use one
> connection to perform a brute-force attack:
>
> Aug 18 00:00:01 aberdeen sshd[87989]: Invalid user serwis from 83.19.113.122
> Aug 18 00:00:03 aberdeen sshd[88010]: Invalid user serwis from 83.19.113.122
> Aug 18 00:00:05 aberdeen sshd[88012]: Invalid user serwis from 83.19.113.122
> Aug 18 00:00:10 aberdeen sshd[88014]: Invalid user serwis from 83.19.113.122
> Aug 18 00:00:13 aberdeen sshd[88019]: Invalid user serwis from 83.19.113.122
> Aug 18 00:00:14 aberdeen sshd[88021]: Invalid user serwis from 83.19.113.122
>
>
It looks as though you need to lower 'MaxAuthTries' in your
sshd_config file, as the default is set to allow six authentication
attempts per connection.

You'll find this in the sshd_config(5) man page.

Scot
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