[CentOS] Re: Email dictionary attacks and firewall

John Hinton webmaster at ew3d.com
Wed Aug 16 19:10:44 UTC 2006


Scott Silva wrote:
> rado spake the following on 8/16/2006 3:49 AM:
>   
>> On Wed, 2006-08-16 at 05:49 -0400, John Hinton wrote:
>>     
>>> I keep seeing 'Joe Average compromised computer on broadband' being used 
>>> to do email dictionary attacks on our systems. Seems I always have 
>>> several domains going through these. One in particular has been in the 
>>> 'a-' list for weeks with about 20,000 attempts per day from various 
>>> systems. Yeah, I do have a system which blocks email from these systems 
>>> for a period of time after 3 bad email address attempts.... throttling...
>>>
>>> Anyway, this brought to mind.... Joe Average! Joe Average buys a 
>>> broadband connection, has someone hook up his computer.. talks to tech 
>>> support about everything and eventually, an AV subscription dies or 
>>> something and Joe just doesn't care or doesn't know how to deal with 
>>> that. Meanwhile Joe's computer gets a virus allowing some baddy to start 
>>> sending email. Joe notices his computer is getting a little slow.. but 
>>> it's not bad enough to worry about.
>>>
>>> So, this made me start wondering about how to do something that makes 
>>> Joe's computer so slow that he finally gives up and calls in tech 
>>> support to fix the damned thing.
>>>
>>> I wonder if there is a way that a firewall rule could be written, that 
>>> would let a trickle of the connection from Joe through, so as his 
>>> dictionary attack gets backed up with a huge number of connections which 
>>> are trickling through at such a slow rate, with maybe just enough delay 
>>> built in to make it keep trying.... Basically making Joe's compromised 
>>> computer useless.. and maybe he'd at least turn it off if it didn't lock 
>>> up all by itself....
>>>
>>> It is so very sad that some providers don't monitor their own people. I 
>>> see where comcast has now slid down to number 8 after holding the number 
>>> one spot as the biggest spammer network for a very long time. Good for 
>>> them! It seems the undisputed king of this world now is 
>>> verizonbusiness.com.... bad bad very bad....
>>>
>>> Sorry.. yeah.. a bit off topic......
>>>
>>> John Hinton
>>>       
> Better would be a rule to forward their connection to a honeypot / tarpit box
> that would do what you want ... tie up their connection for a while.
>   
Yeah... but even Johnny apparently gets hacked. ;)

The fear of retribution or a war is always an important consideration. 
It seems that no matter how big you are, someone can always overload 
your bandwidth. Maybe not if you're google. But even then, a mass attack 
from multiple networks, something I have experienced.. over 1000 
machines hitting an intensive php script once per second... and a crawl 
develops, either due to bandwidth or serverload.

Oh, well... I like to get my log reports to see whose doing what.. it's 
just that these dictionary scripts through so much garbage in among the 
good information.. and I'm getting about 30 megs of logwatch reports per 
day... Not complaining about logwatch, as I know how to turn it down and 
things off.. They just mess up my reports, just like spam messes up an 
inbox.

Best,
John Hinton



More information about the CentOS mailing list