Inline and stream 4

["Pieter Vanmeerbeek" <pieter.vanmeerbeek () able be>]

Hi

I've got a question on a stream 4 configuration. This is our setup: 

All traffic from internet and dmz is routed to snort using iptables QUEUE
statement. All traffic from our router itself and all traffic from the
secure LAN is NOT routed to snort. We are using the upgradeable rule set
with all rules set to drop to have an IPS system

This worked fine, however sometimes connections were dropped without
alerting. After some research I found out that it is the stream4
preprocessor who was doing this. Adding the midstream_drop_alerts parameter
solves the problem however may expose us to snot & stick attacks.

2 questions about this:
 
1. I thought a snot & stick attack was designed to bury a hacking attempt
between other useless attacks and therefore obscure the logging and possible
recognition. But in an IPS system the attack itself is logged and also
blocked. So I do not understand why this is may be a problem?

2. Apparently the problem of question 1 is not an issue if the inline_state
parameter is set. However as we do not send all traffic through snort this
will probably cause a lot of packages to be dropped? Even more general, is
there a possible state problem when only traffic from internet/dmz is routed
to snort? In other words would some rules match due to a state problem?


Kind regards,
Pieter



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