[Oisf-devel] FP on complex netbios sig

[Peter Manev]

Hi,

What happens if you change all the contents ...
content:"|00 5C 00|w|00|i|00|n|00|r|00|e|00|g|
00 00 00|"
change to content:"5C 00 77 00 69 00 ......." so on ?


Thanks

On Wed, Aug 22, 2012 at 1:08 AM, rmkml <rmkml at yahoo.fr> wrote:

> Hi,
>
> First, Congratulations for a new Suricata v1.3.1 !
>
> ok Im test this new version, and I have a complex netbios FP, based on
> this old netbios sig:
>  alert tcp $EXTERNAL_NET any -> $HOME_NET 445 (msg:"NETBIOS SMB-DS winreg
> unicode create tree attempt"; flow:established,to_server;
> flowbits:isset,smb.tree.**connect.ipc; content:"|00|"; depth:1;
> content:"|FF|SMB|A2|"; within:5; distance:3; byte_test:1,&,128,6,relative;
> pcre:"/^.{27}/R"; content:"|5C 00|w|00|i|00|n|00|r|00|e|00|g|**00 00
> 00|"; within:16; distance:51; nocase; flowbits:set,smb.tree.create.**winreg;
> classtype:protocol-command-**decode; sid:2477; rev:6;)
>
>
> ok I small change on this for reply FP with my joigned pcap file: (removed
> established and two flowbits)
>  alert tcp $EXTERNAL_NET any -> $HOME_NET 445 (msg:"NETBIOS SMB-DS winreg
> unicode create tree attempt"; flow:to_server; content:"|00|"; depth:1;
> content:"|FF|SMB|A2|"; within:5; distance:3; byte_test:1,&,128,6,relative;
> pcre:"/^.{27}/R"; content:"|5C 00|w|00|i|00|n|00|r|00|e|00|g|**00 00
> 00|"; within:16; distance:51; nocase; classtype:protocol-command-**decode;
> sid:2477; rev:66;)
>
> ok when I start v1.3.1, suricata fire:
>  06/11/2012-11:51:51.690598  [**] [1:2477:66] NETBIOS SMB-DS winreg
> unicode create tree attempt [**] [Classification: Generic Protocol Command
> Decode] [Priority: 3] {TCP} 172.21.35.149:4345 -> 172.16.142.24:445
> Of course, snort not fire.
>
> ok hexa dump my pcap file:
> #000000C8 13 38 01 0A 96 A7 00 00 00 64 FF 53 4D 42 A2 00 00 00 00 18
> .8.......d.SMB......
> #                            +          ++++ ++++++++   1  2  3  4  5
> #000000DC 07 C8 00 00 67 E1 67 45 78 C7 9C F1 00 00 06 10 B4 16 02 20
> ....g.gEx..........
> #           &128
> #          6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
> #000000F0 80 02 18 FF 00 DE DE 00 0E 00 16 00 00 00 00 00 00 00 9F 01
> ....................
> #         26 27  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17
> #00000104 02 00 00 00 00 00 00 00 00 00 00 00 00 00 03 00 00 00 01 00
> ....................
> #         18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
> #00000118 00 00 40 00 00 00 02 00 00 00 03 11 00 00 5C 00 77 00 69 00
> .. at ...........\.w.i.
> #                                                    ^
> #         38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
> #0000012C 6E 00 72 00 65 00 67 00 00 00 00 00 CC 00 00 00
> n.r.e.g.........
>
>
> Why Suricata fire?
>
> ok modified sig for firing snort with my pcap: (added 0x00 and changed 16
> -> 17)
>  alert tcp $EXTERNAL_NET any -> $HOME_NET 445 (msg:"NETBIOS SMB-DS winreg
> unicode create tree attempt"; flow:to_server; content:"|00|"; depth:1;
> content:"|FF|SMB|A2|"; within:5; distance:3; byte_test:1,&,128,6,relative;
> pcre:"/^.{27}/R"; content:"|00 5C 00|w|00|i|00|n|00|r|00|e|00|g|**00 00
> 00|";
> within:17; distance:51; nocase; classtype:protocol-command-**decode;
> sid:2477; rev:67;)
> and Suricata fire again.
>
> If anyone confirm, Im open a new redmine ticket...
>
> Regards
> Rmkml
>
> http://twitter.com/rmkml
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>



-- 
Regards,
Peter Manev
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