Mercury: network metadata capture and analysis

This package contains two programs for fingerprinting network traffic and capturing and analyzing packet metadata: mercury, a Linux application that leverages the modern Linux kernel's high-performance networking capabilities (AF_PACKET and TPACKETv3), which is described below, and pmercury, a portable python application. There is also a User's Guide. While mercury is used in some production applications, please consider this software as a 'beta'. The CHANGELOG itemizes changes across different versions.

Overview

Mercury reads network packets, identifies metadata of interest, and writes out the metadata in JSON format. Alternatively, mercury can write out the packets that contain the metadata in the PCAP file format. Mercury can scale up to high data rates (40Gbps on server-class hardware); it uses zero-copy ring buffers to acquire packets, and packets are processed by independent worker threads. The amount of memory consumed by the ring buffers, and the number of worker threads, are configurable; this makes it easy to scale up (but be wary of using too much memory).

Mercury produces fingerprint strings for TLS, DTLS, SSH, HTTP, TCP, and other protocols; these fingerprints are formed by carefully selecting and normalizing metadata extracted from packets (as documented here). Fingerprint strings are reported in the "fingerprint" object in the JSON output. Optionally, mercury can perform process identification based on those fingerprints and the destination context; these results are reported in the "analysis" object.

Contents

• Building and installing mercury
  • Installation
  • Compile-time options
• Running mercury
  • Details
  • System
  • Examples
• Ethics
• Credits
• Acknowledgements

Building and installing mercury

Mercury itself has minimal dependencies other than a g++ or llvm build environment, but to run the automated tests and ancillary programs in this package, you will need to install additional packages, as in the following Debian/Ubuntu example: sudo apt install g++ jq git zlib1g-dev tcpreplay valgrind python3-pip libssl-dev clang pip3 install jsonschema To build mercury, in the root directory, run ./configure make to build the package (and check for the programs and python modules required to test it). TPACKETv3 is present in Linux kernels newer than 3.2.

Building mercury on macOS Apple Silicon is currently experimental. Note that on macOS, standalone mercury can read pcap as input but not capture on an interface, since AF_PACKET is Linux-specific. The following has been tested on an M2 mac with Python 3.13.2 installed via the Homebrew command below. brew install python openssl zlib mkdir -p ~/.envs python3 -m venv ~/.envs/merc source ~/.envs/merc/bin/activate python3 -m pip install --upgrade pip python3 -m pip install --upgrade jsonschema cryptography Cython wheel setuptools ./configure && make cd src/cython && make && make wheel

Installation

In the root directory, edit mercury.cfg with the network interface you want to capture from, then run ``` ./configure make

sudo make install MERCURYCFG=mercury.cfg to install mercury and create and start a systemd service. If you don't want the mercury systemd service to be installed, then instead run sudo make install-nosystemd ``` The default file and directory locations are * _/usr/local/bin/mercury__ for the executable * /usr/local/share/mercury for the resource files * /usr/local/var/mercury for the output files * /etc/mercury/mercury.cfg for the configuration file * /etc/systemd/system/mercury.service for the systemd unit file

The output file directory is owned by the user mercury; this user is created by the 'make install' target, which must be run as root. The installation prefix /usr/local/ can be changed by running ./configure with the --prefix argument, for instance `--prefix=$HOME'. If you want to install the program somewhere in your home directory, you probably don't want to create the user mercury; you should use the 'make install-nonroot' target, which does not create a user, does not install anything into /etc, and does not install a systemd unit.

The easiest way to run mercury in capture mode is using systemd; the OS automatically starts the mercury systemd unit after each boot, and halts it when the OS is shut down. To check its status, run systemctl status mercury and the output should contain 'active (running)'. To view the log (stderr) output from the mercury unit, run sudo journalctl -u mercury

To uninstall mercury, run sudo make uninstall which will remove the mercury program, resources directory, user, group, and systemd related files. The directory containing capture files will be retained, but its owner will be changed to root, to avoid unintentional data loss. All captured data files are retained across successive installs and uninstalls, and must be manually deleted.

Compile-time options

To create a debugging version of mercury, use the make debug-mercury target in the src/ subdirectory. Be sure to run make clean first.

There are compile-time options that can tune mercury for your hardware. Each of these options is set via a C/C++ preprocessor directive, which should be passed as an argument to "make" through the OPTFLAGS variable. First run make clean to remove the previous build, then run make "OPTFLAGS=". This runs make, telling it to pass to the C/C++ compiler. The available compile time options are:

• -DDEBUG, which turns on debugging, and
• -FBUFSIZE=16384, which sets the fwrite/fread buffer to 16,384 bytes (for instance). If multiple compile time options are used, then they must be passed to make together in the OPTFLAGS string, e.g. "OPTFLAGS=-DDEBUG -DFBUFSIZE=16384".

Running mercury

``` mercury: packet metadata capture and analysis ./src/mercury [INPUT] [OUTPUT] [OPTIONS]: INPUT [-c or --capture] captureinterface # capture packets from interface [-r or --read] readfile # read packets from file no input option # read packets from standard input OUTPUT [-f or --fingerprint] jsonfilename # write JSON fingerprints to file [-w or --write] pcapfilename # write packets to PCAP/MCAP file no output option # write JSON fingerprints to stdout --capture OPTIONS [-b or --buffer] b # set RXRING size to (b * PHYSMEM) [-t or --threads] [num_threads | cpu] # set number of threads [-u or --user] u # set UID and GID to those of user u [-d or --directory] d # set working directory to d GENERAL OPTIONS --config c # read configuration from file c [-a or --analysis] # analyze fingerprints --resources=f # use resource file f --format=f # report fingerprints with formats(s) f --stats=f # write stats to file f --stats-time=T # write stats every T seconds --stats-limit=L # limit stats to L entries [-s or --select] filter # select traffic by filter (see --help) --nonselected-tcp-data # tcp data for nonselected traffic --nonselected-udp-data # udp data for nonselected traffic --reassembly # reassemble protocol messages over multiple transport segments [-l or --limit] l # rotate output file after l records --output-time=T # rotate output file after T seconds --dns-json # output DNS as JSON, not base64 --certs-json # output certs as JSON, not base64 --metadata # output more protocol metadata in JSON --raw-features # select protocols to write out raw features string(see --help) --minimize-ram # minimize the ram usage of mercury library [-v or --verbose] # additional information sent to stderr --license # write license information to stdout --version # write version information to stdout [-h or --help] # extended help, with examples

DETAILS "[-c or --capture] c" captures packets from interface c with Linux AFPACKET using a separate ring buffer for each worker thread. "[-t or --thread] t" sets the number of worker threads to t, if t is a positive integer; if t is "cpu", then the number of threads will be set to the number of available processors. "[-b or --buffer] b" sets the total size of all ring buffers to (b * PHYSMEM) where b is a decimal number between 0.0 and 1.0 and PHYS_MEM is the available memory; USE b < 0.1 EXCEPT WHEN THERE ARE GIGABYTES OF SPARE RAM to avoid OS failure due to memory starvation.

"[-f or --fingerprint] f" writes a JSON record for each fingerprint observed, which incorporates the flow key and the time of observation, into the file f. With [-a or --analysis], fingerprints and destinations are analyzed and the results are included in the JSON output.

"[-w or --write] w" writes packets to the file w, in PCAP format. With the option [-s or --select], packets are filtered so that only ones with fingerprint metadata are written.

"[r or --read] r" reads packets from the file r, in PCAP format.

if neither -r nor -c is specified, then packets are read from standard input, in PCAP format.

"[-s or --select] f" selects packets according to the metadata filter f, which is a comma-separated list of the following strings: arp ARP message bittorrent Bittorrent Handshake Message, LSD message, DHT message cdp CDP message dhcp DHCP discover message dnp3 DNP3 industrial control message dns DNS messages dtls DTLS clientHello, serverHello, and certificates gre GRE message http HTTP request and response http.request HTTP request http.response HTTP response ftp FTP request and response ftp.request FTP request ftp.response FTP response icmp ICMP message iec IEC 60870-5-104 lldp LLDP message mdns multicast DNS mysql MySQL Client/Server Protocol nbns NetBIOS Name Service nbds NetBIOS Datagram Service nbss NetBIOS Session Service openvpntcp OpenVPN over TCP ospf OSPF message quic QUIC handshake sctp SCTP message ssh SSH handshake and KEX smb SMB v1 and v2 smtp SMTP client and server messages stun STUN messages ssdp SSDP (UPnP) socks SOCKS4,SOCKS5 messages tcp TCP headers tcp.message TCP initial message tcp.synack TCP syn ack message tls TLS clientHello, serverHello, and certificates tls.clienthello TLS clientHello tls.serverhello TLS serverHello tls.certificates TLS serverCertificates tofsee Tofsee malware communication wireguard WG handshake initiation message geneve Geneve encapsulation vxlan VXLAN encapsualtion all all of the above all of the above none none of the above

--nonselected-tcp-data writes the first TCP Data field in a flow with nonzero length, for non-selected traffic, into JSON. This option provides a view into the TCP data that the --select option does not recognize. The --select filter affects the TCP data written by this option; use '--select=none' to obtain the TCP data for each flow.

--nonselected-udp-data writes the first UDP Data field in a flow with nonzero length, for non-selected traffic, into JSON. This option provides a view into the UDP data that the --select option does not recognize. The --select filter affects the UDP data written by this option; use '--select=none' to obtain the UDP data for each flow.

--reassembly enables reassembly This option allows mercury to keep track of tcp or udp segment state and and reassemble these segments based on the application in payload

"[-u or --user] u" sets the UID and GID to those of user u, so that output file(s) are owned by this user. If this option is not set, then the UID is set to SUDO_UID, so that privileges are dropped to those of the user that invoked sudo. A system account with username mercury is created for use with a mercury daemon.

"[-d or --directory] d" sets the working directory to d, so that all output files are written into that location. When capturing at a high data rate, a high performance filesystem and disk should be used, and NFS partitions should be avoided.

"--config c" reads configuration information from the file c.

[-a or --analysis] performs analysis and reports results in the "analysis" object in the JSON records. This option only works with the option [-f or --fingerprint].

"--format=f" reports fingerprints with formats(s) f, where f is either a fingerprint protocol and format like "tls/1", or is a comma separated list of below fingerprint protocol and format strings. tls tls/1 tls/2 quic quic/1

"[-l or --limit] l" rotates output files so that each file has at most l records or packets; filenames include a sequence number, date and time.

--dns-json writes out DNS responses as a JSON object; otherwise, that data is output in base64 format, as a string with the key "base64".

--certs-json writes out certificates as JSON objects; otherwise, that data is output in base64 format, as a string with the key "base64".

--metadata writes out additional metadata into the protocol JSON objects.

--raw-features selects protocols to write out raw features string into the protocol JSON object which can be comma separated list of following strings: bittorrent Bittorrent Handshake Message, LSD message, DHT message smb SMB v2, v3 messages ssdp SSDP (UPnP) stun Stun messages tls TLS clientHello all All of the above none None of the above None of the above

--minimize-ram minimizes the ram usage of mercury library by reducing classifer features and minimizing the maximum reassembly segments."

[-v or --verbose] writes additional information to the standard error, including the packet count, byte count, elapsed time and processing rate, as well as information about threads and files.

--license and --version write their information to stdout, then halt.

[-h or --help] writes this extended help message to stdout. ```

SYSTEM

The directories used by the default install are as follows. Run mercury --help to see if the directories on your system differ. Resource files used in analysis: /usr/local/share/mercury Systemd service output: /usr/local/var/mercury Systemd service configuration /etc/mercury/mercury.cfg

EXAMPLES

mercury -c eth0 -w foo.pcap # capture from eth0, write to foo.pcap mercury -c eth0 -w foo.pcap -t cpu # as above, with one thread per CPU mercury -c eth0 -w foo.mcap -t cpu -s # as above, selecting packet metadata mercury -r foo.mcap -f foo.json # read foo.mcap, write fingerprints mercury -r foo.mcap -f foo.json -a # as above, with fingerprint analysis mercury -c eth0 -t cpu -f foo.json -a # capture and analyze fingerprints

Ethics

Mercury is intended for defensive network monitoring, security research and forensics. Researchers, administrators, penetration testers, and security operations teams can use these tools to protect networks, detect vulnerabilities, and benefit the broader community through improved awareness and defensive posture. As with any packet monitoring tool, Mercury could potentially be misused. Do not run it on any network of which you are not the owner or the administrator.

Credits

Mercury and this package was developed by David McGrew, Brandon Enright, Blake Anderson, Lucas Messenger, Adam Weller, Andrew Chi, Shekhar Acharya, Anastasiia-Mariia Antonyk, Oleksandr Stepanov, Vigneshwari Viswanathan, and Apoorv Raj, with input from Brian Long, Bill Hudson, and others. Pmercury was developed by Blake Anderson, with input from others.

Acknowledgments

This package includes GeoLite2 data created by MaxMind, available from https://www.maxmind.com.

We make use of Mozilla's Public Suffix List which is subject to the terms of the Mozilla Public License, v. 2.0.

This package directly incorporates some software made by other developers, to make the package easier to build, deploy, and run. We are grateful to the copyright holders for making their excellent software available under licensing terms that allow its redistribution. * RapidJSON https://github.com/cisco/mercury/blob/main/src/libmerc/rapidjson/license.txt; this package is Copyright 2015 THL A29 Limited, a Tencent company, and Milo Yip. * lctrie https://github.com/cisco/mercury/tree/main/src/libmerc/lctrie; this package is copyright 2016-2017 Charles Stewart