[Bro] Large outbound transfer

scott mcallester scott at 0x4c.com
Tue Mar 25 20:31:33 PDT 2014

I have, but it uses the connection_state_remove event, and the more I think about it, the more I think it wouldn't work.
If someone manages to gain access to our file server, zips up 10-20gb of our files and starts transferring this out, I dont think this event would fire until the connection closes, which would be too late, but here it is anyway: 

@load base/frameworks/notice

module DataExfiltration;

export {
        redef enum Notice::Type += {data_exfiltration_100mb};

event connection_state_remove(c: connection)
          if (c$orig$num_bytes_ip > 102400000 && c$orig$num_pkts > 1000) {
                  #test for internal to external

                          if( ! Site::is_local_addr(c$id$resp_h)){
                $msg="> 100mb of data sent out in a single connection",


And this in local.bro:

@load DataExfiltration
hook Notice::policy(n: Notice::Info) {
  if ( n$note == DataExfiltration::data_exfiltration_100mb )
      add n$actions[Notice::ACTION_EMAIL];
      n$email_body_sections[|n$email_body_sections|] = fmt("Service:
%s\nData sent: %s\nData received: %s", join_string_set(n$conn$service,
","), n$conn$orig$size, n$conn$resp$size );

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