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On 6/27/07 10:39 PM, Daniel Ouellet wrote:
quoted text
> Steve B wrote:
>> The rule I've had in my pf.conf file to catch and block forceful SSH
>> attempts no longer appears to be working. I see the entries in my
>> authlog,
>> but the IPs are no longer getting added to my table. I suspect I screwed
>> something  up, but so far I am at a loss to see where. Could someone pass
>> another set of eyes over the relevant parts of my pf.conf?
> 
> Put quickly as an example, but you can try:
> 
> # Define some variable for clarity
> SSH_LIMIT="(max-src-conn-rate 3/30, overload <scanners> flush global)"
> 
> ## SSH Hackers - blocked IPs
> table <scanners> persist file "/etc/tables/scanners"
> 
> # Block ssh access to bad ssh scanner
> block drop in log quick on $ext_if inet proto tcp \
>    from <scanners> to any port ssh
> 
> # Allow quick valid traffic to ssh but log all attempts as well
> pass in log quick on $ext_if inet proto tcp from ! <scanners> \
>    to $ext_if port ssh flags S/SA keep state \
>    $SSH_LIMIT
> 

I've added something like this to pf.conf but it's only partially
successful. I would appreciate any clues as to why it's not blocking all
brute-force attempts.

On an OBSD 4.1 box, here's what I added to pf.conf ($unpro is the
Internet-facing interface):

#####

# Define limit of ssh connection rates
SSH_LIMIT="(max-src-conn-rate 3/30, overload <scanners> flush global)"
# SSH scanners - blocked IPs
table <scanners> persist

block drop in log quick on $unpro inet proto tcp \
  from <scanners> to any port ssh


# Allow quick valid traffic to ssh but log all attempts as well
pass in log quick on $unpro inet proto tcp from ! <scanners> \
   to $unpro port ssh $SSH_LIMIT

#####

And it appears to be working, at least in part:

dnewman@fw17 ~ 501$ sudo pfctl -t scanners -T show
   61.146.178.13
   61.189.145.103
   67.76.237.190
   161.200.144.108
   193.254.31.194

#####

But some hosts on the protected side of the firewall still report
brute-force ssh login attempts exceeding the 3/30 rate:

Aug  7 10:16:00 mail sshd[21608]: Invalid user trash from 201.18.81.8
Aug  7 10:16:08 mail sshd[21610]: Invalid user aaron from 201.18.81.8
Aug  7 10:16:11 mail sshd[21612]: Invalid user gt05 from 201.18.81.8
Aug  7 10:16:18 mail sshd[21614]: Invalid user william from 201.18.81.8
Aug  7 10:16:22 mail sshd[21616]: Invalid user stephanie from 201.18.81.8
Aug  7 10:16:59 mail sshd[21628]: Invalid user gary from 201.18.81.8
Aug  7 10:17:07 mail sshd[21632]: Invalid user guest from 201.18.81.8
Aug  7 10:17:11 mail sshd[21634]: Invalid user test from 201.18.81.8
Aug  7 10:17:17 mail sshd[21636]: Invalid user oracle from 201.18.81.8
Aug  7 10:19:24 mail sshd[21717]: Invalid user apache from 201.18.81.8
Aug  7 10:19:43 mail sshd[21723]: Invalid user lab from 201.18.81.8
Aug  7 10:19:55 mail sshd[21729]: Invalid user oracle from 201.18.81.8
Aug  7 10:20:00 mail sshd[21736]: Invalid user svn from 201.18.81.8
Aug  7 10:20:06 mail sshd[21745]: Invalid user iraf from 201.18.81.8
Aug  7 10:20:13 mail sshd[21747]: Invalid user swsoft from 201.18.81.8
Aug  7 10:20:18 mail sshd[21749]: Invalid user production from 201.18.81.8
Aug  7 10:20:23 mail sshd[21751]: Invalid user guest from 201.18.81.8
Aug  7 10:20:28 mail sshd[21753]: Invalid user gast from 201.18.81.8
Aug  7 10:20:34 mail sshd[21755]: Invalid user gast from 201.18.81.8
Aug  7 10:20:40 mail sshd[21762]: Invalid user oliver from 201.18.81.8
Aug  7 10:20:45 mail sshd[21767]: Invalid user sirsi from 201.18.81.8
Aug  7 10:20:50 mail sshd[21769]: Invalid user nagios from 201.18.81.8
Aug  7 10:20:55 mail sshd[21771]: Invalid user nagios from 201.18.81.8
Aug  7 10:20:59 mail sshd[21773]: Invalid user nagios from 201.18.81.8

Thanks in advance for suggestions as to how to reduce these kind of
login attempts.

dn
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