[Snort-users] false positive rules in snort 2.8.6.0

Safwat Fahmy safwat.fahmy at ...14822...
Fri Jun 4 16:57:17 EDT 2010


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 at ...1935...] 
Sent: Friday, June 04, 2010 4:32 PM
To: Will Metcalf
Cc: snort-users at 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 at ...1935...> 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
>> 
>> 
>> 
>>
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>> 
>> 
>> --
>> Joel Esler
>> 302-223-5974
>> Jabber: jesler at ...1935...
>> 
>>
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--
Joel Esler
302-223-5974
Jabber: jesler at ...1935...


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ThinkGeek and WIRED's GeekDad team up for the Ultimate 
GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the 
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