Snort mailing list archives

Re: how to stop these UDP TCP alerts?


From: jlarsson () altavoz net
Date: Wed, 24 Sep 2003 13:20:26 -0400 (CLT)

I have scanned through mailinglists looking for which "false alerts" these TCP  
checks will stop.   I get the following messages in my alert file  
  
(snort_decoder): Short UDP packet, length field > payload length  
(snort_decoder) WARNING: TCP Header length exceeds packet length!  
(snort_decoder): Truncated Tcp Options  
  
where can i find an explanation of what these means "Stop generic decode event",  
"Stop alerts on experimental TCP options", etc.  
  
/Johan 
 
PS, Sorry to have sent this two times to you Erek :( 
 
Quoting Erek Adams <erek () snort org>: 
 
On Mon, 22 Sep 2003, Clayton Mascarenhas wrote: 
 
I know this question has been asked before, but I cannot find the 
answer 
to this. I have really searched google and the mailing list but still 
cant find the answer to this question. 

Could I please know how to stop snort 2.0.2 from generating the 
following alerts... 

[**] (snort_decoder): Short UDP packet, length field > payload length 
[**] 01/29-01:00:18.399475 132.x.x.x:0 -> 132.x.x.x:0 UDP TTL:128 
TOS:0x0 ID:15667 IpLen:20 DgmLen:161Len: 133 

[**] (snort_decoder) WARNING: TCP Header length exceeds packet 
length! 
[**]01/29-01:00:09.082724 132.x.x.x:0 -> 132.x.x.x:0 TCP TTL:60 
TOS:0x0 
ID:57434 IpLen:20 DgmLen:52 DF ***A**** Seq: 0x21676561 Ack: 
0xCECE0987 
Win: 0xC036 TcpLen: 32 

I am getting a million of these alerts. I dont think there is any 
snort 
rule to this. Am I correct? 
 
They are from the 'snort_decoder', not from a rule. 
 
To stop them you'll have to either use a BPF filter to ignore the 
hosts, 
or turn off the TCP checks in the snort.conf (there's a whole section 
on 
it). 
 
Cheers! 
 
----- 
Erek Adams 
 
   "When things get weird, the weird turn pro."   H.S. Thompson 
 
 
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