[Snort-users] TCP Reset

Erik Engberg Erik.Engberg at ...511...
Tue May 22 07:09:26 EDT 2001

My few cents on TCP kill/reset.

Pretty much useless for most DoS, BoF and anything else that can be spoofed.
Problem: They can be triggered to annoy a third party network and can waste
resources and bandwidth. Besides, you can never ever be sure it's not
spoofed to start with and that an attacker will "honor" a reset.
You need the IDS to function as a firewall or bridge and intercept the
packets to be effective against these kinds of threats. Or use the
functionality of Syn defender/Syn gateway/Syn proxy or whatever your
firewall vendor calls it.

TCP resets can be effective in certain cases:

To kill unencrypted established connections like telnet, smtp, ftp etc where
a prepetrator tries to do su, sudo, VRFY, EXPN, illegal SITE commands etc. 
Same goes for "keywords" in URLs, on webpages etc... (I´d recommend to use
another app to filter that).
Or why not kill backdoor traffic? Or kill unwanted traffic types on an
internal net where it's not practical with a firewall (get behind me

Wan't your machine to ignore resets? filter it out with your favourite
firewall (ipfilter in my case) or reconfigure your kernel to not give a damn
about them...
However, it won't be to helpful as a tcpkill should go to both machines in a


-----Original Message-----
From: michael.porter at ...1284... [mailto:michael.porter at ...1284...]
Sent: Saturday, May 19, 2001 9:51 PM
To: Snort Users Mailing List
Subject: [Snort-users] TCP Reset


What does the group think of the benefits of killing TCP connections, as 
available in FLEXRESP, or even the Tcpkill feature in ISS Realsecure?

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