[Oisf-devel] FP on complex netbios sig

[rmkml]

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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