Re: Inline and stream 4

["Will Metcalf" <william.metcalf () gmail com>]

Are you seeing a TWH handshake when you try to initiate your
connections?  Or are you just seeing one side of the conversation? 
Fire up tcpdump and tell it to listen on your bridge interface.  Which
side of the conversation is retransmitting data?  Add a -j LOG rule to
the end of your FORWARD chain, is the traffic that you are expecting
to show up in snort bypassing your QUEUE rules?

Regards,

Will

On 4/20/06, Pieter Vanmeerbeek <pieter.vanmeerbeek () able be> wrote:
> We have a whole range of iptables rules. In fact it is a system were every
> rule resides in a chain. This way we can always jump to one specific rule.
> Whenever a rule accepts a packet it is send to special chains _INP_ACCEPT or
> _FWD_ACCEPT or _OUT_ACCEPT chain dependant of the table. Only when the
> incoming device is lo the packet is directly accepted as this is a local
> communication.
>
> (pkts bytes target     prot opt in     out     source
> destination
> 57536 8916K ACCEPT     all  --  lo     *       0.0.0.0/0
> 0.0.0.0/0 )
>
>
> In these special chains a jump to the _IPS chain is made, in which the
> actual jump to QUEUE is made, this is the _IPS chain:
>
> Chain _IPS (2 references)
>  pkts bytes target     prot opt in     out     source
> destination
>  224K  187M QUEUE      all  --  *      *       0.0.0.0/0
> 0.0.0.0/0           condition ips_runs
>
>
>
> This is a conditional jump which is controlled by the
> /proc/net/ipt_condition/ips_run flag.
>
>
> As far as I can tell the packets are send correctly to snort. I checked this
> by starting an ssh session from the server to something in the lan, snort
> shows the packet with the sync bit on when started with the -v option.
>
> When an ACCEPT jump is placed in the _IPS chain before the queue statement
> or when the ips_run flags is set to 0 the ssh session works again.
>
>
>
>
> Kind regards,
> Pieter
>
>
>
> -----Original Message-----
> From: Will Metcalf [mailto:william.metcalf () gmail com]
> Sent: donderdag 20 april 2006 15:12
> To: Pieter Vanmeerbeek
> Cc: snort-users () lists sourceforge net
> Subject: Re: [Snort-users] Inline and stream 4
>
> can you send us a scrubbed version of your iptables rules?
>
> Regards,
>
> Will
>
> On 4/20/06, Pieter Vanmeerbeek <pieter.vanmeerbeek () able be> wrote:
> > Hi,
> >
> > As indicated in my previous post we were only sending incoming traffic
> from
> > the Internet and DMZ devices through snort.
> >
> > Following your advise I tried to route all traffic through snort, this is
> > our setup
> >
> >
> > INT -- Server with snort -- LAN
> >
> >
> >
> > I created a jump to QUEUE in iptables in the output, forward and input
> > table, in other words all combination .
> >
> > However from the moment a jump in the output table is set, it isn't
> possible
> > to make connections, I tested this with an ssh session from the LAN  to
> the
> > server and a session from the server to the LAN.
> >
> > I debugged the last one, running snort with the -v option shows me that
> > packets are sent to snort as they are logged, however dumping on the
> secure
> > lan device of the server shows no packets. Disabling the jump to the QUEUE
> > statement solves the problem. For some reason a ping to the lan and to the
> > server seem to work, so I don't think everything is blocked.
> >
> > I can't seem to find the problem as no alerts are shown. I tried removing
> > all rules and even all preproccessors from the snort.conf file but still
> the
> > same problem. I set the home_net variable to the secure lan IP address and
> > internet IP address. I used the default snort.conf file with http_inspect
> > disabled and the stream4 midstream_drop_alerts option on. All rules are
> set
> > to drop, but as the problem still exists without any rules in the
> snort.conf
> > I don't think a problem exists there.
> >
> > Is there anything else I can disable/enable to see something more? I even
> > tried a small program that reads its input from the QUEUE user land end
> > which just passes its input on. Using this program everything seems to
> work.
> > Kind regards,
> > Pieter
> >
> >
> >
> >
> > -----Original Message-----
> > From: snort-users-admin () lists sourceforge net
> > [mailto:snort-users-admin () lists sourceforge net] On Behalf Of Pieter
> > Vanmeerbeek
> > Sent: donderdag 13 april 2006 12:20
> > To: snort-users () lists sourceforge net
> > Subject: [Snort-users] Inline and stream 4
> >
> > 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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