Re: 1337 Bot and TCP options detection

[FOULDE Damien <damien.foulde () axians com>]

Joshua,

 

To be able to match on the |01 03 03 07| content in the TCP header and then
use the “flags” keyword you could split the rule and set a flowbit
(http://blog.snort.org/2011/05/resolving-flowbit-dependancies.html) in a
first snort ip rule and check this flowbit in a second snort tcp rule.

 

Regards,

 

Damien

 

De : FOULDE Damien 
Envoyé : mercredi 28 décembre 2016 15:23
À : 'joshua burgess'
Cc : snort-sigs () lists sourceforge net
Objet : RE: 1337 Bot and TCP options detection

 

Hello Joshua,

 

You may write an ip rule, not a tcp one, to be able to match on the |01 03
03 07| content in the TCP header.

However writing the snort rule through this way will prevent you to use the
“flags” keyword reserved for the tcp rules.

 

Regards,

 

Damien

 

De : joshua burgess [mailto:avonyxx () hotmail com] 
Envoyé : mercredi 28 décembre 2016 13:51
À : snort-sigs () lists sourceforge net
Objet : [Snort-sigs] 1337 Bot and TCP options detection

 

To check a few boxes, I'm trying to gen up two signatures designed to detect
the latest 1337 bot that Imperva wrote about
(https://www.incapsula.com/blog/650gbps-ddos-attack-leet-botnet.html)

 

Basically I'm trying to write a signature designed to detect the TCP options
which spell out 1337 as well as an abnormally large SYN packet ranging from
799 to 936. 

 

I don't know SNORT supports my specifying the TCP options like:

Number: No-Operation (NOP) (1)

Kind: Window Scale (3)

Length: (3)

Shift count: (7)

 

Could I do it with"content" only, it doesn't seem likely but I'm running out
of ideas...

alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"1337 DDoS Tool"; flags:S;
content:"Number: No-Operation (NOP) (1)"; content:"Kind: Window Scale (3)";
content:"Length: (3)"; content:"Shift count: (7)";
reference:url,https://www.incapsula.com/blog/650gbps-ddos-attack-leet-botnet
.html; classtype:attempted-dos; sid:6000049; rev:1;)

 

As far as writing a signature to look for just the SYN packet size would
this work to set two different sizes? 

 

alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"1337 DDoS Tool"; flags:S;
dsize:>799; dsize:<936;
reference:url,https://www.incapsula.com/blog/650gbps-ddos-attack-leet-botnet
.html; classtype:attempted-dos; sid:6000049; rev:1;)

 

Any help would be awesome. Thanks!

 

Sent from Outlook <http://aka.ms/weboutlook>

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