machine hangs on occasion - correlated with ssh
julian at elischer.org
Thu Aug 21 20:42:44 UTC 2008
Kevin Oberman wrote:
>> Date: Thu, 21 Aug 2008 13:38:38 -0400
>> From: Mikhail Teterin <mi+mill at aldan.algebra.com>
>> Sender: owner-freebsd-stable at freebsd.org
>> A machine I manage remotely for a friend comes under a distributed ssh
>> break-in attack every once in a while. Annoyed (and alarmed) by the
>> messages like:
>> Aug 12 10:21:17 symbion sshd: Invalid user mythtv from 188.8.131.52
>> Aug 12 10:21:18 symbion sshd: Invalid user mythtv from 184.108.40.206
>> Aug 12 10:21:20 symbion sshd: Invalid user mythtv from 220.127.116.11
>> Aug 12 10:21:21 symbion sshd: Invalid user mythtv from 18.104.22.168
>> I wrote an awk-script, which adds a block of the attacking IP-address to
>> the ipfw-rules after three such "invalid user" attempts with:
>> ipfw add 550 deny ip from ip
>> The script is fed by syslogd directly -- through a syslog.conf rule
>> Once in a while I manually flush these rules... I this a good (safe)
>> I'm asking, because the machine (currently running 7.0 as of July 7)
>> hangs solid once every few weeks... My only guess is that a spike in
>> attacks causes "too many" ipfw-entries created, which paralyzes the
>> kernel due to some bug -- the machine is running natd and is the gateway
>> for the rest of the network...
>> The hangs could, of course, be caused by something else entirely, but my
>> self-defense mechanism is my first suspect...
>> Any comments? Thanks!
also, if you do this, have a single rule that uses a table
and add the addresses to the table.
> Looks remarkably like sshguard (ports/security/sshguard-*). It does almost
> exactly what you are doing but is written in C and has command-line
> switches to set how long a system is blocked, how many attempts
> constitute an attack and how long it should remember failed attempts. It
> also allows the use of back-end scripts if you want it to do something
> else such as generate reports (beyond an entry in /var/log/messages).
> As far as the hangs, I don't believe it is from the large nu,ber of
> brute force attempts as they will stop for a given host as soon as the
> firewall is updated. I seldom see more than a handful of attack sources
> over any short period.
> Should you want to continue with your own tool, at least for IPv4,
> consider using tables rather than a raft of rules. With tables, you need
> only a single rule and it is there at boot time.
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