ICSNPP-BACnet

Industrial Control Systems Network Protocol Parsers (ICSNPP) - BACnet.

Overview

ICSNPP-BACnet is a Zeek plugin for parsing and logging fields within the BACnet protocol.

This plugin was developed to be fully customizable. To drill down into specific BACnet packets and log certain variables, users can add the logging functionality to scripts/icsnpp/bacnet/main.zeek. The functions within scripts/icsnpp/bacnet/main.zeek and src/events.bif are good guides for adding new logging functionality.

This parser produces four log files. These log files are defined in scripts/icsnpp/bacnet/main.zeek.

• bacnet.log
• bacnet_discovery.log
• bacnet_property.log
• bacnet_device_control.log

For additional information on these log files, see the Logging Capabilities section below.

Installation

Package Manager

This script is available as a package for Zeek Package Manger

zkg refresh
zkg install icsnpp-bacnet

If this package is installed from ZKG it will be added to the available plugins. This can be tested by running zeek -N. If installed correctly, users will see ICSNPP::BACnet.

If ZKG is configured to load packages (see @load packages in quickstart guide), this plugin and these scripts will automatically be loaded and ready to go. ZKG Quickstart Guide

If users are not using site/local.zeek or another site installation of Zeek and want to run this package on a packet capture, they can add icsnpp/bacnet to the command to run this plugin's scripts on the packet capture:

git clone https://github.com/cisagov/icsnpp-bacnet.git
zeek -Cr icsnpp-bacnet/tests/traces/bacnet_example.pcap icsnpp/bacnet

Manual Install

To install this package manually, clone this repository and run the configure and make commands as shown below.

git clone https://github.com/cisagov/icsnpp-bacnet.git
cd icsnpp-bacnet/
./configure
make

If these commands succeed, users will end up with a newly created build directory. This contains all the files needed to run/test this plugin. The easiest way to test the parser is to point the ZEEK_PLUGIN_PATH environment variable to this build directory.

export ZEEK_PLUGIN_PATH=$PWD/build/
zeek -N # Ensure everything compiled correctly and you are able to see ICSNPP::BACnet

Once users have tested the functionality locally and it appears to have compiled correctly, they can install it system-wide:

sudo make install
unset ZEEK_PLUGIN_PATH
zeek -N # Ensure everything installed correctly and you are able to see ICSNPP::BACnet

To run this plugin in a site deployment users will need to add the line @load icsnpp/bacnet to the site/local.zeek file to load this plugin's scripts.

If users are not using site/local.zeek or another site installation of Zeek and want to run this package on a packet capture, they can add icsnpp/bacnet to the command to run this plugin's scripts on the packet capture:

zeek -Cr icsnpp-bacnet/tests/traces/bacnet_example.pcap icsnpp/bacnet

If users want to deploy this on an already existing Zeek implementation and don't want to build the plugin on the machine, they can extract the ICSNPP_Bacnet.tgz file to the directory of the established ZEEK_PLUGIN_PATH (default is ${ZEEK_INSTALLATION_DIR}/lib/zeek/plugins/).

tar xvzf build/ICSNPP_Bacnet.tgz -C $ZEEK_PLUGIN_PATH 

Logging Capabilities

BACnet Header Log (bacnet.log)

Overview

This log captures BACnet header information for every BACnet/IP packet and logs it to bacnet.log. BACnet has two different protocol data layer messages (PDUs) - Application Protocol Data Unit (APDU) and Network Protocol Data Unit (NPDU). Both APDU and NPDU messages are logged to bacnet.log, but fields captured and logged are slightly different as seen below.

Fields Captured (BACnet-APDU Packets)

Fields Captured (BACnet-NPDU Packets)

Discovery Log (bacnet_discovery.log)

Overview

This log captures important fields for Who-Is, I-Am, Who-Has, and I-Have messages and logs them to bacnet_discovery.log.

Fields Captured

Property Log (bacnet_property.log)

Overview

This log captures important variables for Read-Property-Request, Read-Property-ACK, and Write-Property-Request messages and logs them to bacnet_property.log.

Fields Captured

Device Control Log (bacnet_device_control.log)

Overview

This log captures important variables for Reinitialize-Device and Device-Communication-Control messages and logs them to bacnet_device_control.log.

Fields Captured

Source and Destination Fields

Overview

Zeek's typical behavior is to focus on and log packets from the originator and not log packets from the responder. However, most ICS protocols contain useful information in the responses, so the ICSNPP parsers log both originator and responses packets. Zeek's default behavior, defined in its id struct, is to never switch these originator/responder roles which leads to inconsistencies and inaccuracies when looking at ICS traffic that logs responses.

The default Zeek id struct contains the following logged fields:

• id.orig_h (Original Originator/Source Host)
• id.orig_p (Original Originator/Source Port)
• id.resp_h (Original Responder/Destination Host)
• id.resp_p (Original Responder/Destination Port)

Additionally, the is_orig field is a boolean field that is set to T (True) when the id_orig fields are the true originators/source and F (False) when the id_resp fields are the true originators/source.

To not break existing platforms that utilize the default id struct and is_orig field functionality, the ICSNPP team has added four new fields to each log file instead of changing Zeek's default behavior. These four new fields provide the accurate information regarding source and destination IP addresses and ports:

• source_h (True Originator/Source Host)
• source_p (True Originator/Source Port)
• destination_h (True Responder/Destination Host)
• destination_p (True Responder/Destination Port)

The pseudocode below shows the relationship between the id struct, is_orig field, and the new source and destination fields.

if is_orig == True
    source_h == id.orig_h
    source_p == id.orig_p
    destination_h == id.resp_h
    destination_p == id.resp_p
if is_orig == False
    source_h == id.resp_h
    source_p == id.resp_p
    destination_h == id.orig_h
    destination_p == id.orig_p

Example

The table below shows an example of these fields in the log files. The first log in the table represents a Modbus request from 192.168.1.10 -> 192.168.1.200 and the second log represents a Modbus reply from 192.168.1.200 -> 192.168.1.10. As shown in the table below, the id structure lists both packets as having the same originator and responder, but the source and destination fields reflect the true source and destination of these packets.

BACnet File Extraction

BACnet contains two messages for sending and receiving files: Atomic-Read-File and Atomic-Write-File. This plugin will extract files sent via these two messages and pass the extracted files to Zeek's file analysis framework.

Troubleshooting

By default, this BACnet parser uses a Zeek DPD signature to detect BACnet traffic. If users are seeing false positives in their BACnet logs and their BACnet traffic is operating on UDP port 47808, users can disable this DPD signature by removing or commenting-out the first line of scripts/icsnpp/bacnet/__load__.zeek.

Default configuration, parses BACnet traffic on all UDP ports, but may produce false positives

@load-sigs ./dpd.sig
@load ./main
@load ./files

Modified configuration, only parses BACnet traffic on UDP/47808:

# @load-sigs ./dpd.sig
@load ./main
@load ./files

ICSNPP Packages

All ICSNPP Packages:

• ICSNPP

Full ICS Protocol Parsers:

• BACnet
  • Full Zeek protocol parser for BACnet (Building Control and Automation)
• BSAP
  • Full Zeek protocol parser for BSAP (Bristol Standard Asynchronous Protocol) over IP
  • Full Zeek protocol parser for BSAP Serial comm converted using serial tap device
• Ethercat
  • Full Zeek protocol parser for Ethercat
• Ethernet/IP and CIP
  • Full Zeek protocol parser for Ethernet/IP and CIP
• Genisys
  • Full Zeek protocol parser for Genisys
• OPCUA-Binary
  • Full Zeek protocol parser for OPC UA (OPC Unified Architecture) - Binary
• S7Comm
  • Full Zeek protocol parser for S7comm, S7comm-plus, and COTP
• Synchrophasor
  • Full Zeek protocol parser for Synchrophasor Data Transfer for Power Systems (C37.118)
• Profinet IO CM
  • Full Zeek protocol parser for Profinet I/O Context Manager

Updates to Zeek ICS Protocol Parsers:

• DNP3
  • DNP3 Zeek script extending logging capabilities of Zeek's default DNP3 protocol parser
• Modbus
  • Modbus Zeek script extending logging capabilities of Zeek's default Modbus protocol parser

License

Copyright 2023 Battelle Energy Alliance, LLC. Released under the terms of the 3-Clause BSD License (see LICENSE.txt).