[CentOS] A new attack

Aleksandar Milivojevic alex at milivojevic.org
Fri Nov 10 16:54:09 UTC 2006

Quoting John Hinton <webmaster at ew3d.com>:

> David Ellsmore wrote:
>> John Hinton wrote:
>>> Log report is reporting a lot of these lately.. following is just   
>>> a short snippet from the beginning on one server.
>>> WARNING!!!!
>>> Possible Attack:
>>>  Attempt from 104.29.broadband2.iol.cz [] with:
>>>     command=HELO/EHLO, count=3 : 1 Time(s)
>>>  Attempt from 106.7.broadband7.iol.cz [] with:
>>>     command=HELO/EHLO, count=3 : 1 Time(s)
>>>  Attempt from 106.74.broadband5.iol.cz [] with:
>>>     command=HELO/EHLO, count=3 : 1 Time(s)
>>>  Attempt from 126.239.broadband7.iol.cz [] with:
>>>     command=HELO/EHLO, count=3 : 1 Time(s)
>>>  Attempt from 144.Red-80-34-151.staticIP.rima-tde.net [] with:
>>>     command=HELO/EHLO, count=3 : 1 Time(s)
>>> Could anyone expand on what these folks are actually doing? And if  
>>>  I should be concerned?
>> To me it looks like something/someone looking for valid email   
>> addresses - perhaps to use in an effort to defeat spam filters.   
>> It'd be interesting to see what sort of conversation takes place   
>> between your server and the attacker, and how close together time   
>> wise these are occuring.
>> I notice the first 5 warnings are from the Czech Republic, and the   
>> last one is from Spain. Are you getting these from world wide   
>> addresses or just these two countries?
> I just snipped out the first five so as not to clog the list. They are
> mostly coming from the baltic region of the world (what the heck
> country is a .il tld?)... a lot from that one. But also a fair
> representation from the largest spamming network in the world.. verizon
> who doesn't care one bit

The .il TLD is Israel.

> Almost in every case, they are making three attempts.. but I have
> sendmail set to pause receiving from a network after 2 bad attempts, so
> maybe this would be worse without that entry? I don't really know the
> flow of attempts like this on my system.

Just ignore them.  If you were to increase logging level, you'd see  
that first two attempts were either empty or using URL-like argument  
precded by a bar (attempts EHLO, than HELO).  After that it reattempts  
with real host name, but by that time the count gets to three and  
Sendmail logs the warning.

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