Re: Looking for info on Flowbits

[Matt Jonkman <mjonkman () infotex com>]

I don't have a detailed analysis of flowbits for you, but if you look at
these sigs you'll have the info you need to understand the sig you're
looking at:

POLICY/POLICY_Non-Standard_SSH_Port:#alert tcp any any -> any $SSH_PORTS
(msg: "BLEEDING-EDGE POLICY SSHv2 Client New Keys detected on Expected
Port"; flowbits:noalert; flowbits:isset,is_ssh_client_kex; flow:
from_client,established; byte_test:1,=,21,5;flowbits: set,is_proto_ssh;
classtype:misc-activity; sid: 2001977; rev:6; )

POLICY/POLICY_Non-Standard_SSH_Port:alert tcp any any -> any !$SSH_PORTS
(msg: "BLEEDING-EDGE POLICY SSHv2 Client New Keys Detected on Unusual
Port"; flowbits:isset,is_ssh_client_kex; flowbits:noalert; flow:
from_client,established; byte_test:1,=,21,5; flowbits: set,is_proto_ssh;
classtype:misc-activity; sid: 2001983; rev:6; )

These two will set the var is_proto_ssh, but not generate an alert. That
will set the stage for the sig you're looking at.

Matt

dajackman wrote:
> I am interested in reading more about the flowbits option.  I have
> poked around a little on the net and haven't satisfied my curiosity. 
> Does any one know a good writup/doc on the flowbit and or the flow
> preprocessor.  What started my search was trying to understand how the
> below rule works.  Thanks for any help
>
>
> alert tcp any any <> any !$SSH_PORTS (msg: "BLEEDING-EDGE POLICY SSH
> session in progress on Unusual Port"; flowbits: isset,is_proto_ssh;
> threshold: type both, track by_src, count 2, seconds 300;
> classtype:misc-activity; sid: 2001984; rev:4; )
>
>
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