known_*.log and software.log

Zeek produces several logs that help summarize certain aspects of the network it monitors. These logs track a few aspects of the local network, such as SSL/TLS certificates, host IP addresses, services, and applications.

The sections which follow will present examples of entries in known_certs.log, known_hosts.log, known_services.log, and software.log files collected on live networks.

For full details on each field of those log files, see Known::CertsInfo, Known::HostsInfo, Known::ServicesInfo, and Software::Info.


The known_certs.log captures information about SSL/TLS certificates seen on the local network. Here is one example:

  "ts": "2020-12-31T15:15:53.690221Z",
  "host": "",
  "port_num": 443,
  "subject": "L=San Jose,ST=CA,O=Ubiquiti Networks,CN=UBNT Router UI,C=US",
  "issuer_subject": "L=San Jose,ST=CA,O=Ubiquiti Networks,CN=UBNT Router UI,C=US",
  "serial": "98D0AD47D748CDD6"

This example shows a device offering a TLS server on port 443 TCP, with a certificate associated with Ubiquiti Networks.


The known_hosts.log simply records a timestamp and an IP address when Zeek observes a new system on the local network.


This edited example shows how this log could be part of an IP address inventory program.


The known_services.log records a timestamp, IP, port number, protocol, and service (if available) when Zeek observes a system offering a new service on the local network. Here is what a single entry looks like:

  "ts": "2021-01-03T01:19:36.242774Z",
  "host": "",
  "port_num": 53,
  "port_proto": "udp",
  "service": [

For the following list, I used the jq utility to remove the timestamp but show the other log values.


Note how many of the services do not have names associated with them.


Zeek’s software.log collects details on applications operated by the hosts it sees on the local network. The log captures information like the following:

  "ts": "2021-01-03T00:16:22.694616Z",
  "host": "",
  "software_type": "HTTP::BROWSER",
  "name": "Windows-Update-Agent",
  "version.major": 10,
  "version.minor": 0,
  "version.minor2": 10011,
  "version.minor3": 16384,
  "version.addl": "Client",
  "unparsed_version": "Windows-Update-Agent/10.0.10011.16384 Client-Protocol/2.0"

It is amazing in 2021 that so many modern applications still use clear text protocols subject to collection and analysis by software like Zeek.

Services beyond HTTP may also reveal interesting details. Consider these three entries:

["","SSH::SERVER","OpenSSH",6,6,1,null,"p1","OpenSSH_6.6.1p1 Debian-4~bpo70+1"]
["","SSH::CLIENT","OpenSSH",6,6,1,null,"p1","OpenSSH_6.6.1p1 Debian-4~bpo70+1"]

These examples show an SSH server and two different SSH clients.


Details recorded in known_certs.log, known_hosts,log, known_services.log, and software.log files can help network and security analysts better understand the nature of the activity in their environment. Some of this information relies on capturing clear text, while other aspects are based solely on the presence of the services and hosts on the network.