[Bro] Implementing a new script
Seth Hall
seth at icir.org
Wed Jul 13 08:25:57 PDT 2016
Hi Connor,
This is a nice job at a first script. I'll point out a few issues I noticed with it, but generally I think you got pretty close to what you wanted.
Bro won't have detected the protocol in the connection yet in the new_connection event. Generally you can assume that no payload has been seen when the new_connection event is generated which means that we don't yet know if the traffic is encrypted or not. :) You could use the protocol_violation event to watch for the SSL analyzer to be violated. Port 443/tcp always gets the SSL analyzer attached as a heuristic but it will fail if the traffic is not actually SSL. This might actually be the most straightforward mechanism.
https://www.bro.org/sphinx/scripts/base/bif/event.bif.bro.html#id-protocol_violation
One other tiny mistake is that you're comparing the c$conn$service field against "SSL" but the value in the service field will be "ssl". You just need to fix your casing.
Nice script!
.Seth
> On Jul 12, 2016, at 3:26 PM, Connor Borchgrevink <borchgrevink at aggienetwork.com> wrote:
>
> Howdy all,
>
> I recently began poking around Bro and had my first attempt of writing a script. The purpose of it was to detect whether or not traffic on port 443 used SSL, the moment I implemented the script my CPU usage was at 100% and the same happened to my memory. Without the script enabled, the machine runs fine and bro only uses about 50-60% of the resources. I also tried to turn off every other thing in local.bro but it was the same result. The code is as follows (be warned its pretty rough):
>
> @load base/protocols/ssl
> @load base/frameworks/notice
> @load base/protocols/conn
> @load base/utils/directions-and-hosts
>
> module conn;
>
> export {
> redef enum Notice::Type += {
> Unencrypted_Traffic
> };
>
> const List_of_Hosts = LOCAL_HOSTS &redef;
> const Encryption = "SSL" &redef;
> }
>
> event new_connection(c: connection) &priority=3
> {
> if ( ! addr_matches_host(c$id$resp_h, List_of_Hosts) )
> return;
>
> local port_number=c$conn$id$resp_p;
> local ip_address=c$conn$id$resp_h;
> local encrypted=c$conn$service;
>
> if ( port_number != 443/tcp )
> return;
>
> if ( encrypted != Encryption )
> NOTICE([$note=Unencrypted_Traffic,
> $msg=fmt("Unencrypted traffic"),
> $conn=c,
> $identifier=cat(c$id$resp_h, c$id$resp_p)
> ]);
> }
>
>
> It is probably something I am not catching in my code or a limited knowledge of bro, but any help is much appreciated.
>
> Thanks
>
> Connor
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--
Seth Hall
International Computer Science Institute
(Bro) because everyone has a network
http://www.bro.org/
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