Re: Network hardware IPS

[Cory Stoker <cstoker () latis com>]

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Alvin Wong wrote:

<snip>

|
|Also, my question to any is the following
|"One note of caution on TCP Reset is not a preferred method of blocking
|attacks according to some security experts. " Alan Shimel
|
|Why isn't TCP reset a preferred method of blocking?
|
|Regards,
|Alvin
|
<snip>

Hi:

The main reason that TCP resets are not a preferred method of blocking 
is it is not Guaranteed to be successful.  I quote below:

" In our tests, snort (v 1.8.4 and beta v. 1.9.1) does not always kill 
the HTTP connection using the RST and/or ICMPs. In most of the cases 
connection is reset and sometimes it remains running and the file (dummy 
" cmd.exe" placed on Apache web server) is successfully downloaded. The 
possible explanation is that RST arrives too late for the connection to 
be reset since the response from server comes earlier with the right 
sequence number. The delayed RST is then discarded. Thus RST/ICMP is not 
a reliable security mechanism (exactly as claimed in the snort 
documentation)." -- Anton Chuvakin, Ph.D.

Also many attacks are too short for a TCP reset to be effective or the 
attacker could change his IP stack to disregard the TCP reset.

Thanks,
- --

Cory Stoker
Security Engineer
Latis Networks, Inc.

www.stillsecure.com
Reducing your risk has never been this easy

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