One of our reader submitted some DSL Modem Firewall logs (iptables format) and I wrote a simple logstash parser to analyze and illustrate the activity, in this case it is all scanning activity against this modem. An iptables parser exist for Filebeat[2], but for this example, I wanted to show how to create a simple logstash parser using Grok[3] to parse these logs and send them to Elastic.

# Guy Bruneau, guybruneau.com

# Date: 13 Feb 2021

# Version: 0.1

#

# Parse to Elastic Common Schema (ECS) format

# #

# This custom parser is parsing iptables type firewall logs dump data

# Grab the logs file from filebeat which match the pattern /home/guy/logs

Now that the data is in Elasticsearch, I can create various reports based on the activity logged by iptables. The dashboards I prepared shows the number of records, the Top 10 targeted ports (services) and a table with the Top 10 sources with its location (GeoIP), action taken by the firewall and a total.

It is always a good idea to monitor and review the activity logged by the modem. If you aren't sure what to look for, we have tips published here as well as how you can participate and submit your logs to DShield, the service is open and free.

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Guy Bruneau IPSS Inc.

My Handler Page

Twitter: GuyBruneau

gbruneau at isc dot sans dot edu

Source: Sans.edu

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