ICSNPP-S7COMM

Industrial Control Systems Network Protocol Parsers (ICSNPP) - s7comm, s7comm-plus, and COTP.

Overview

ICSNPP-S7COMM is a Zeek plugin for parsing and logging fields within the s7comm, s7comm-plus, and COTP protocols.

This plugin was developed to be fully customizable. To drill down into specific packets and log certain variables, users can add the logging functionality to scripts/icsnpp/s7comm/main.zeek. The functions within scripts/icsnpp/s7comm/main.zeek and src/events.bif are good guides for adding new logging functionality.

This parser currently produces five log files. These log files are defined in scripts/icsnpp/s7comm/main.zeek.

• cotp.log
• s7comm.log
• s7comm_read_szl.log
• s7comm_upload_download.log
• s7comm_plus.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-s7comm

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, you will see ICSNPP::S7COMM.

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/s7comm to the command to run this plugin's scripts on the packet capture:

git clone https://github.com/cisagov/icsnpp-s7comm.git
zeek -Cr icsnpp-s7comm/tests/traces/s7comm_plus_example.pcap icsnpp/s7comm

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-s7comm.git
cd icsnpp-s7comm/
./configure
make

If these commands succeed, you will end up with a newly create 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::S7COMM

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::S7COMM

To run this plugin in a site deployment, users will need to add the line @load icsnpp/s7comm 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/s7comm to the command to run this plugin's scripts on the packet capture:

zeek -Cr icsnpp-s7comm/tests/traces/s7comm_plus_example.pcap icsnpp/s7comm

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_S7comm.tgz file to the directory of the established ZEEK_PLUGIN_PATH (default is ${ZEEK_INSTALLATION_DIR}/lib/zeek/plugins/).

tar xvzf build/ICSNPP_S7comm.tgz -C $ZEEK_PLUGIN_PATH 

Logging Capabilities

COTP Log (cotp.log)

Overview

This log captures COTP information for every COTP packet and logs it to cotp.log.

Fields Captured

Field	Type	Description
ts	time	Timestamp
uid	string	Unique ID for this connection
id	conn_id	Default Zeek connection info (IP addresses, ports)
is_orig	bool	True if the packet is sent from the originator
source_h	address	Source IP address (see Source and Destination Fields)
source_p	port	Source port (see Source and Destination Fields)
destination_h	address	Destination IP address (see Source and Destination Fields)
destination_p	port	Destination port (see Source and Destination Fields)
pdu_code	string	COTP PDU type code (in hex)
pdu_name	string	COTP PDU name

S7COMM Header Log (s7comm.log)

Overview

This log captures s7comm header information for every s7comm packet and logs it to s7comm.log.

Fields Captured

Field	Type	Description
ts	time	Timestamp
uid	string	Unique ID for this connection
id	conn_id	Default Zeek connection info (IP addresses, ports)
is_orig	bool	True if the packet is sent from the originator
source_h	address	Source IP address (see Source and Destination Fields)
source_p	port	Source port (see Source and Destination Fields)
destination_h	address	Destination IP address (see Source and Destination Fields)
destination_p	port	Destination port (see Source and Destination Fields)
rosctr_code	count	Remote operating service control code (in hex)
rosctr_name	string	Remote operating service control name
pdu_reference	count	Reference ID used to link requests to responses
function_code	string	Parameter function code (in hex)
function_name	string	Parameter function name
subfunction_code	string	User-Data subfunction code (in hex)
subfunction_name	string	User-Data subfunction name
error_class	string	Error class name
error_code	string	Error code within error class

S7COMM Read-SZL Log (s7comm_read_szl.log)

Overview

This log captures information for the common S7Comm Read-SZL function. This data is logged to s7comm_read_szl.log.

Fields Captured

Field	Type	Description
ts	time	Timestamp
uid	string	Unique ID for this connection
id	conn_id	Default Zeek connection info (IP addresses, ports)
is_orig	bool	True if the packet is sent from the originator
source_h	address	Source IP address (see Source and Destination Fields)
source_p	port	Source port (see Source and Destination Fields)
destination_h	address	Destination IP address (see Source and Destination Fields)
destination_p	port	Destination port (see Source and Destination Fields)
pdu_reference	count	Reference ID used to link requests to responses
method	string	Request or response
szl_id	string	SZL ID (in hex)
szl_id_name	string	Meaning of SZL ID
szl_index	string	SZL index (in hex)
return_code	string	Return code (in hex)
return_code_name	string	Meaning of return code

S7COMM Upload-Download Log (s7comm_upload_download.log)

Overview

This log captures information for the S7Comm Upload and Download functions (see list below). This data is logged to s7comm_upload_download.log:

• Start Upload
• Upload
• End Upload
• Request Download
• Download Block
• Download Ended

Fields Captured

Field	Type	Description
ts	time	Timestamp
uid	string	Unique ID for this connection
id	conn_id	Default Zeek connection info (IP addresses, ports)
is_orig	bool	True if the packet is sent from the originator
source_h	address	Source IP address (see Source and Destination Fields)
source_p	port	Source port (see Source and Destination Fields)
destination_h	address	Destination IP address (see Source and Destination Fields)
destination_p	port	Destination port (see Source and Destination Fields)
rosctr	count	Remote operating service control
pdu_reference	count	Reference ID used to link requests to responses
function_code	count	Parameter function code
function_status	count	Function status
session_id	count	Session ID
blocklength	count	Length of block to upload/download
filename	string	Filename of block to upload/download
block_type	string	Block type to upload/download
block_number	string	Block number to upload/download
destination_filesystem	string	Destination filesystem of upload/download

S7COMM-PLUS Log (s7comm_plus.log)

Overview

This log captures s7comm-plus header information for every s7comm-plus packet and logs it to s7comm_plus.log.

Fields Captured

Field	Type	Description
ts	time	Timestamp
uid	string	Unique ID for this connection
id	conn_id	Default Zeek connection info (IP addresses, ports)
is_orig	bool	True if the packet is sent from the originator
source_h	address	Source IP address (see Source and Destination Fields)
source_p	port	Source port (see Source and Destination Fields)
destination_h	address	Destination IP address (see Source and Destination Fields)
destination_p	port	Destination port (see Source and Destination Fields)
version	count	S7comm-plus version
opcode	string	Opcode code (in hex)
opcode_name	string	Opcode name
function_code	string	Opcode function code (in hex)
function_name	string	Opcode function name

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.

id.orig_h	id.orig_p	id.resp_h	id.resp_p	is_orig	source_h	source_p	destination_h	destination_p
192.168.1.10	47785	192.168.1.200	502	T	192.168.1.10	47785	192.168.1.200	502
192.168.1.10	47785	192.168.1.200	502	F	192.168.1.200	502	192.168.1.10	47785

S7COMM File Extraction

S7COMM contains two functions for sending and receiving files: Upload and Download-Block. This plugin will extract files sent via these two functions and pass the extracted files to Zeek's file analysis framework.

Coverage

See Logging Capabilities for detailed information of the parser coverage.

S7Comm is a proprietary protocol which makes coverage information and statistics difficult to compose. All coverage details in this section include information and statistics based on the S7Comm and S7Comm plus traffic observed in test networks and publicly available packet captures.

General/Header Logging

The general log files for COTP (cotp.log), S7Comm (s7comm.log), and S7Comm Plus (s7comm_plus.log) contain basic header information for all known (~100%) COTP, S7Comm and S7Comm Plus messages.

Detailed Logging

Detailed logging for 1 S7comm function is logged in the read szl log file (s7comm_read_szl.log), 6 S7Comm functions are logged in the upload download log file (s7comm_upload_download.log), and 5 S7comm functions are logged as part of the general S7comm log file (s7comm.log). ~30% of known S7comm functions contain detailed logging.

There is currently no (0%) detailed logging for S7Comm Plus functions outside of the S7Comm Plus general/header log file (s7comm_plus.log).

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
• GE SRTP
  • Full Zeek protocol parser for GE SRTP
• 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).