Re: false positive rules in snort 2.8.6.0

["Safwat Fahmy" <safwat.fahmy () safemedia com>]

Joel and Will:

Just an example of the KAD problem This is one of the captor points( I do
not know how to write rules for snort YET)

1st capture point for KAD:
OUTGOING PACKET ONLY TCP
Offset  0       1       2       3       4       5
Hex     0xe3    sz      sz      0x00    0x00    0x01
Match on bytes(0,3to 5);;;Extended Mandatory Match on Mesg. Length: (sz=
Data length -5) 
At the end of Mesg. Length either the packet will end or e3,e4,e5 or c5 byte
will be found.
payload length > 25


for Emule:
OUTGOING +INCOMING      
0th byte        1st byte        2nd byte        Mandatory Mesg. Len.
Mesh. Type
e3      sz      sz      compute(refer 1A)       TCP

and:

OUTGOING +INCOMING   USED 
e3      0a      none    25 bytes        UDP
e3      0c      none    25 bytes        UDP
e3      96      none    6 bytes UDP
e3      a2      none    6 bytes UDP


I wish I know how to write snort rules...I would have written those rule for
the group.

Safwat



-----Original Message-----
From: Joel Esler [mailto:jesler () sourcefire com] 
Sent: Friday, June 04, 2010 4:32 PM
To: Will Metcalf
Cc: snort-users () lists sourceforge net
Subject: Re: [Snort-users] false positive rules in snort 2.8.6.0

Wait, before we get into all of that...  Are we sure you are running in
"inline" mode?


On Jun 4, 2010, at 4:28 PM, Will Metcalf wrote:

> Ummmm so what is happening is that these rules are written to
> fingerprint a protocol.  If I remember correctly dropping the traffic
> identified by these sigs isn't enough to cripple e-mule.  Detection !=
> Prevention...  Another example.. fire up a sniffer and and use a tcp
> session splicing attack in InlineMode() against a target...  By the
> time snort does reassembly the packets have already gone across the
> wire.
>
> Regards,
>
> Will
>
> On Fri, Jun 4, 2010 at 3:10 PM, Joel Esler <jesler () sourcefire com> wrote:
> > Okay, so you aren't saying they are falsing, you are saying that the
rules
> > aren't dropping the traffic?
> >
> > On Jun 4, 2010, at 4:00 PM, Lawrence R. Hughes, Sr. wrote:
> >
> > Joel,
> >
> > Thanks for the quick reply...
> >
> > Although they are drop rules, the clients in both cases connect, allow
> > searches and downloads.
> >
> > We do not use pcap, we thought that snort's coverage was enough.
> >
> > Our main concern is about the RIAA...
> >
> > Thanks,
> > Larry
> >
> >
> > ----- Original Message -----
> > From: Joel Esler
> > To: Lawrence R. Hughes, Sr.
> > Sent: Friday, June 04, 2010 3:55 PM
> > Subject: Re: [Snort-users] false positive rules in snort 2.8.6.0
> > What are they falsing on?  Do you have a pcap?
> > J
> > On Jun 4, 2010, at 3:50 PM, Lawrence R. Hughes, Sr. wrote:
> >
> > Hi All,
> >
> > The following two (2) rules in p2p.rules are false positives... Be aware
of
> > the RIAA
> >
> > drop tcp $HOME_NET 4711 -> $EXTERNAL_NET any (msg:"P2P eDonkey server
> > response"
> >  flow:established,from_server; content:"Server|3A| eMule";
> >  fast_pattern:only; metadata:policy security-ips drop;
> >  reference:url,www.emule-project.net; classtype:policy-violation;
> >  sid:2587; rev:4;)
> > drop udp $HOME_NET any -> $EXTERNAL_NET 41170
> > (msg:"P2P Manolito Search Query"; flow:to_server; content:"|01 02 00
14|";
> >  depth:4; offset:16; metadata:policy security-ips drop;
> >  reference:url,openlito.sourceforge.net; reference:url,www.blubster.com;
> >  classtype:policy-violation; sid:3459; rev:5;)
> >
> >
> > Thanks,
> > Larry
----------------------------------------------------------------------------
--
> > ThinkGeek and WIRED's GeekDad team up for the Ultimate
> > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the
> > lucky parental unit.  See the prize list and enter to win:
http://p.sf.net/sfu/thinkgeek-promo_________________________________________
______
> > Snort-users mailing list
> > Snort-users () lists sourceforge net
> > Go to this URL to change user options or unsubscribe:
> > https://lists.sourceforge.net/lists/listinfo/snort-users
> > Snort-users list archive:
> > http://www.geocrawler.com/redir-sf.php3?list=snort-users
> >
> > --
> > Joel Esler
> > 302-223-5974
> > Jabber: jesler () sourcefire com
> >
> >
> > --
> > Joel Esler
> > 302-223-5974
> > Jabber: jesler () sourcefire com
----------------------------------------------------------------------------
--
> > ThinkGeek and WIRED's GeekDad team up for the Ultimate
> > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the
> > lucky parental unit.  See the prize list and enter to win:
> > http://p.sf.net/sfu/thinkgeek-promo
> > _______________________________________________
> > Snort-users mailing list
> > Snort-users () lists sourceforge net
> > Go to this URL to change user options or unsubscribe:
> > https://lists.sourceforge.net/lists/listinfo/snort-users
> > Snort-users list archive:
> > http://www.geocrawler.com/redir-sf.php3?list=snort-users

--
Joel Esler
302-223-5974
Jabber: jesler () sourcefire com


----------------------------------------------------------------------------
--
ThinkGeek and WIRED's GeekDad team up for the Ultimate 
GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the 
lucky parental unit.  See the prize list and enter to win: 
http://p.sf.net/sfu/thinkgeek-promo
_______________________________________________
Snort-users mailing list
Snort-users () lists sourceforge net
Go to this URL to change user options or unsubscribe:
https://lists.sourceforge.net/lists/listinfo/snort-users
Snort-users list archive:
http://www.geocrawler.com/redir-sf.php3?list=snort-users


------------------------------------------------------------------------------
ThinkGeek and WIRED's GeekDad team up for the Ultimate 
GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the 
lucky parental unit.  See the prize list and enter to win: 
http://p.sf.net/sfu/thinkgeek-promo
_______________________________________________
Snort-users mailing list
Snort-users () lists sourceforge net
Go to this URL to change user options or unsubscribe:
https://lists.sourceforge.net/lists/listinfo/snort-users
Snort-users list archive:
http://www.geocrawler.com/redir-sf.php3?list=snort-users