bro-is-darknet

Bro Is Darknet?

This plugin adds a Site::is_darknet function. This is useful for scripts that track scan attempts or other probes. It can handle purely dark address space as well as honeynet space.

Configuration.

Mode

is_darknet can operate in four different modes by redefing Site::darknet_mode to one of these values:

  • DARKNET - Only hosts defined in darknet_address_space are dark
  • NOT_ALLOCATED - Only hosts NOT listed in used_address_space are dark
  • DARKNET_OR_NOT_ALLOCATED - Only hosts defined in darknet_address_space OR NOT listed in used_address_space are dark. Useful if you reuse part of darknet space for honey net purposes
  • DARKNET_AND_NOT_ALLOCATED - Only hosts both defined in darknet_address_space AND NOT listed in used_address_space are dark. Useful if your networking group may reallocate your darknet subnets out from under you.

subnet sets

is_darknet uses two sets to determine if an address is darknet or not

  • used_address_space: set[subnet] - A set containing subnets from local_nets that are in use
  • darknet_address_space: set[subnet] - A set containing subnets from local_nets that are dark

You should redef these in local.bro using something like

redef Site::used_address_space = {
    192.168.1.0/24, 192.168.2.0/24, 192.168.4.0/24,
    192.168.10.0/24, 192.168.11.0/24, 192.168.13.0/24,
};

or

redef Site::darknet_address_space = {
    192.168.0.0/24, 192.168.253.0/24, 192.168.2544.0/24,
};

Auto used_address_space tracking

This plugin will also add any host that it sees a bidirectional connection from to used_address_space. It does this by first aggregating the address up to the subnet it was seen in using the v4_aggregation_bits (default 24) or v6_aggregation_bits (default 64) values.

This is for the extra paranoid configuration of darknet_mode = DARKNET_AND_NOT_ALLOCATED. If you have 192.168.0.0/24 listed under darknet_address_space, but bro sees a bidirectional connection to 192.168.0.55 it will no longer treat all of 192.168.0.0/24 as dark.

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