[Snort-users] Snort+flexresp

Onie Camara neil at ...4898...
Thu Mar 28 20:46:10 EST 2002


su-2.05a# snort -V

-*> Snort! <*-
Version 1.8.4 (Build 99)
By Martin Roesch (roesch at ...1935..., www.snort.org)

I'm running it on a FreeBSD-STABLE 4.5.

----- Original Message -----
From: "Bamm Visscher" <bamm at ...539...>
To: "Onie Camara" <neil at ...4898...>
Cc: <snort-users at lists.sourceforge.net>
Sent: Thursday, March 28, 2002 10:23 PM
Subject: Re: [Snort-users] Snort+flexresp


> What version of snort are you running?
>
> Bammkkkk
>
> On Thu, 2002-03-28 at 19:14, Onie Camara wrote:
> > Hi Bamm,
> >
> > It worked when I modified resp:rst_all.  I placed a space after resp:
> >
> > But flex-resp, from my testing, only sometimes kill my tcp session.
> >
> > alert tcp $HOME_NET any -> $EXTERNAL_NET 21 (msg:"FTP access from
> > anonymous"; flags:!R ; resp: rst_all;content:"anonymous";
> > classtype:not-suspicious; sid:1717; rev:2;)
> >
> > So when i ftp to somewhere from the commandline, right after pressing
Enter
> > key on the anonymous entry on username,
> > I get disconnected. I got impressed with that. But I tried it again, it
> > allowed me to login.
> >
> > I tried both rst_all and rst_snd, same behavior.
> >
> > So looks like, flex-resp code is not ready for production.
> >
> >
> > ----- Original Message -----
> > From: "Bamm Visscher" <bamm at ...539...>
> > To: "Onie Camara" <neil at ...4898...>
> > Cc: <snort-users at lists.sourceforge.net>
> > Sent: Thursday, March 28, 2002 6:04 PM
> > Subject: Re: [Snort-users] Snort+flexresp
> >
> >
> > > Neil,
> > >
> > > Try logging all the packets associated with your session and look to
see
> > > that there are RESETs being sent. It should work.
> > >
> > > Bammkkkk
> > >
> > > On Thu, 2002-03-28 at 09:50, Onie Camara wrote:
> > > > Ok. I created a rule.
> > > >
> > > > alert tcp $HOME_NET any -> $EXTERNAL_NET 21 (msg:"FTP access from
> > > > anonymous"; flags:!R ; resp:rst_all;content:"anonymous";
> > > > classtype:not-suspicious; sid:1717; rev:2;)
> > > >
> > > > And here is the log:
> > > >
> > > > [**] [1:1717:2] FTP access from anonymous [**]
> > > > [Classification: Not Suspicious Traffic] [Priority: 3]
> > > > 03/28-09:45:49.271952 192.168.0.112:1062 -> 129.128.5.191:21
> > > > TCP TTL:64 TOS:0x10 ID:60673 IpLen:20 DgmLen:68 DF
> > > > ***AP*** Seq: 0xF518481  Ack: 0x678EB95E  Win: 0x8218  TcpLen: 32
> > > > TCP Options (3) => NOP NOP TS: 11758512 213343883
> > > >
> > > > You mentioned that flex-resp is friendly to ssh, ftp, .etc. How come
my
> > > > session
> > > > wasn't kill by my rule?
> > > >
> > > > What's wrong with my rule? I even tried it with flags: A+, still
didn't
> > > > work.
> > > > But I still admin that I am not good on those flags.
> > > >
> > > > Thank you.
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Bamm Visscher" <bamm at ...539...>
> > > > To: "Ronneil Camara" <ronneilc at ...4042...>
> > > > Cc: <snort-users at lists.sourceforge.net>
> > > > Sent: Wednesday, March 27, 2002 7:06 AM
> > > > Subject: RE: [Snort-users] Snort+flexresp
> > > >
> > > >
> > > > > Neil,
> > > > >
> > > > > There is no way to force flex-resp to be successful against HTTP.
Most
> > > > > of the time, the source of an HTTP connection sends five packets.
Two
> > > > > for establishing the session (syn then ack), and two to tear down
the
> > > > > session (fin/ack and ack). Plus one that contains the GET/POST/etc
> > > > > request (usually a push/ack). It is impossible for flex-resp to
kill
> > > > > this session before the dest gets the GET/POST/etc, and thus it is
> > > > > impossible to create a rule to prevent the server from processing
the
> > > > > GET/POST/etc request. If for some reason, the GET/POST/etc
contains so
> > > > > much data that it is spread across multiple packets, then you may
have
> > a
> > > > > slim chance at killing the session before the dest processes the
> > request
> > > > > (may the network lag be with you).
> > > > >
> > > > > The dest is going to send as many packets as it takes to return
the
> > info
> > > > > requested, but killing the connection at that time is almost
pointless
> > > > > since the server has already processed the perps request/command.
At
> > > > > best you might prevent the perp from seeing all the results of a
> > > > > directory listing.
> > > > >
> > > > > BTW, this is not a snort specific problem. It affect every IDS
using
> > > > > tcp-resets to kill connections.
> > > > >
> > > > > Bammkkkk
> > > > >
> > > > >
> > > > > On Wed, 2002-03-27 at 00:36, Ronneil Camara wrote:
> > > > > > Hi Bamm,
> > > > > >
> > > > > > I got impressed on how you answered your every post on this
thread.
> > > > > > So now, what can you suggest me so that flex-resp will be
successful
> > on
> > > > > > killing connections let say for http?
> > > > > >
> > > > > > Thank you very much.
> > > > > >
> > > > > > Neil
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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> > >
> >
> >
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