NAME
labrea.conf - labrea(1) configuration file
SYNOPSIS
nnn.nnn.nnn.nnn [- nnn.nnn.nnn.nnn] EXC
nnn.nnn.nnn.nnn [- nnn.nnn.nnn.nnn] HAR
nnn.nnn.nnn.nnn[/nn] IPI
nnnnn [- nnnnn] POR
nnnnn [- nnnnn] PMN
DESCRIPTION
Generalities
labrea.conf is the configuration file for the labrea(1) program.
Each line consists of a selector field, followed by an action verb.
Whitespace is suppressed. Blank lines are ignored, as are lines
beginning with "#".
Selectors
IPs can be specified as either a single address (e.g. "192.168.0.4") or
as a range of addresses (e.g. "192.168.0.1 - 192.168.0.50").
Ports can be specified as either a single port (e.g. 12345) or as a
range of ports (e.g. 1-65535).
IP Capturing
When labrea sees an ARP request for an unused IP, it does the
following:
On an IP by IP basis, store a time and an originating IP address:
1. For an incoming ARP request, check the current time:
a. If currently stored time is 0 or the arp comes from a
different address than the one stored, then store the
current time and the requesting IP and return.
b. If the stored time is less than "-r" seconds ago, ignore
it and return.
c. If currently stored time is more than a minute ago, store
0, return. (Max timeout)
d. Otherwise, grab the IP.
2. See an ARP reply, set stored time to 0.
When an ARP request for a particular IP goes unanswered for longer than
its "rate" setting (default: 3 seconds), labrea crafts an ARP reply
that routes all traffic destined for the IP to a "bogus" MAC address.
labrea listens for TCP/IP traffic routed to that MAC address and then
responds to any SYN packet (ie incoming connection) with a SYN/ACK
packet.
Explanation of terms
Excluded IPs: Are those IPs that labrea should never capture. Note that
automatic mechanisms are also used to prevent capturing IPs with an
active machine on it. See labrea(1) for more details.
Hard captured IPs: The -h --hard-capture option instructs labrea that
once it captures an IP address, then it needn’t wait for a "-r" timeout
the next time around. These IPs are said to be "hard" captured.
Hard excluded IPS: These are IPs that should never be "hard" captured.
In other words, each time there is an ARP request for this IP, then
labrea will always wait for the timeout -r secs before responding.
Tarpitting: On a captured IP, labrea responds to an incoming SYN
connection attempt with a SYN/ACK. This causes the remote machine’s
stack to initiate the Tcp connection and then waste time fruitlessly
trying to continue the conversation.
Persist state capture: labrea can permanently capture connect attempts
by closing the TCP window to force the connection into "persist" state.
In this state, the connection never times out, and labrea hangs on to
the incoming connection until it is closed from the other end.
To accomplish this, short packets are sent every so often to say "keep
waiting, my Tcp window is still closed". So a maximum b/w control is
implemented to limit the total b/w consumption. (see the -p --max-rate
startup option)
Auto hard capturing: This is a startup option that says that unless an
IP is excluded or hard-excluded, then mark it as being hard captured.
This is normally a risky thing to do and should be used with caution.
Normal virtual machine behaviour
Default port behaviour: Incoming connections on any port will be
subject to tarpitting / persist capturing.
Since all connections are inbound, there should be no incoming
SYN/ACKs. Labrea will respond RST to an incoming SYN/ACK unless the
startup option -a --no-resp-synack disables this behaviour.
Excluded ports: Ports that are specifically excluded will not be
tarpitted or persist captured.
Incoming connection attempts on an excluded port will receive a RST.
Virtual machine behaviour when firewalling:
Active ports: When firewalling (i.e. -f --no-resp-excluded-ports) is
active, then by default only the most widely used ports are active at
startup.
Incoming connections on these active ports will be tarpitted and/or
persist captured as usual.
Excluded ports: When firewalling is active, incoming connections on
excluded ports will not receive a response. The packets will be
dropped.
Among other things, this means that nmap scans take much more time to
complete.
Other ports: Ports that are neither active nor excluded are passively
monitored for incoming SYN activity. At startup, they behave as an
excluded port (i.e. packets are dropped).
However, if there is enough activity on a given port, it will
dynamically become active. The threshold is more than 6 SYNs for a
given port in an hour. However every 15 minutes, the port’s SYN count
is reduced by 1 to eliminate noise.
If the SYN count for a port finally reaches 255, then the port is
considered permanently active.
USAGE
This section describes the configuration statements and their usage:
nnn.nnn.nnn.nnn [- nnn.nnn.nnn.nnn] EXC
Never capture the specified IP addresses. This applies to local
IP addresses (i.e. on the local capture netblock) only.
nnn.nnn.nnn.nnn [- nnn.nnn.nnn.nnn] HAR
WHen "hard capturing" is in effect ("-h"), then never hard
capture the specified IP addresses. (i.e. Always wait for the
ARP timeout before responding.) Applies to local IP addresses
only.
nnn.nnn.nnn.nnn[/nn] IPI
Ignore any packets with source IP address in the specified
netblock. labrea will not tarpit or persist capture connections
from the specified IP addresses.
Note that this statement can apply to any IP address.
Note also that the netblock is specified in CIDR notation (ie
nnn.nnn.nnn.nnn/nn) and not as a range of IP addresses.
nnnnn [- nnnnn] POR
These ports are excluded. labrea will not tarpit / persist
capture incoming connections on these ports. A RST will be
returned unless firewalling is active. In that case, the
incoming packet will be dropped.
nnnnn [- nnnnn] PMN
At startup, mark the indicated ports as being active. Incoming
connections to these ports are subject to tarpitting / persist
capturing.
This configuration statement is useful only when firewalling is
active. The port becomes immediately active, instead of waiting
for enough SYNs to bump the port’s SYN count above the activity
threshold.
EXAMPLES
Suppose that the capture subnet is 192.168.10.0/24.
Exclude 192.168.10.5 through .7 from being captured:
192.168.10.5 - 192.168.10.7 EXC
"Hard exclude" 192.168.10.100:
192.168.10.100 HAR
Do not attempt to tarpit / persist capture packets from the class C
subnet 10.2.3.x:
10.2.3.0/24 IPI
Put in some comments:
#
# This is a comment
#
Do not tarpit / persist capture on ports 21-25:
21-25 POR
When firewalling, make port 12345 active at startup:
12345 PMN
FILES
/usr/local/etc/labrea.conf
Default configuration file on unix systems
(current directory) LaBrea.cfg
Default configuration file on Windows systems
SEE ALSO
labrea(1)
AUTHOR
Tom Liston <tliston@hackbusters.net> Bugs: lorgor@users.sourceforge.net
or http://labrea.sourceforge.net