[Snort-users] Snort+flexresp

Bamm Visscher bamm at ...539...
Thu Mar 28 16:06:10 EST 2002


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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