[Snort-sigs] I need a rule for synk4.c attack

Wirth, Jeff WirthJe at ...511...
Wed Apr 10 08:51:08 EDT 2002


Ali,

<snip>
> How can I write a snort (snort 1.8.6) rule for the synk4.c syn flood 
> (with spoofed IP) attack program ?
> 
> Here is the tcpdump of the attack:(destination port 80 supplied as an 
> argument)
> cat TCP\:1368-80
> 04/09-17:05:43.860348 10.10.10.10:1368 -> 10.15.0.27:80
> TCP TTL:30 TOS:0x0 ID:29579 IpLen:20 DgmLen:40
> 1*****S* Seq: 0x28376839  Ack: 0x0  Win: 0xFFFF  TcpLen: 20

Flags set = S (SYN) and 1 (Reserve bit)

> 
> I have tried the above rule to detect the attack, but It doesn't 
> recognize it (I have changed the sequence number of the original rule)
> 
> alert tcp $HOME_NET any <> $EXTERNAL_NET any (msg:"DDOS shaft 
> synflood"; 
> flags: S; seq: 674719801; reference:arachnids,253; 
> classtype:attempted-dos; sid:241; rev:2;)
> 

Shouldn't the flags option be: "flags: 1S" 

- Jeff




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