2018-04-05

Typosquatting Detection with ELK & Bro NSM

Typosquatting Detection Using Elastic ELK & Bro NSM


DNS... I hope as network defenders we all know the value of it. Some may not, as my technical/CND lead once told me "so what its just DNS". If thats the case here is a short list:
From the ability to cheaply block common malware/C2's, content related to at work law-suits, and SSL (via the hostname lookup). Just as commonly as it can be used to "defend" it is a great tool to proactively block malicious ad redirects (by blocking advertisement domains) or dynamic DNS. Yes...There was a time were you could simply block many "APT" groups by blocking dynamic DNS lookups.
However outside of a purely "defensive" standpoint the importance of DNS logs to be able to detect DNS exfil, DGA bot (simple way via nxdomain, sometimes more complex is required), and DNS as a C2 channel -- as well as (retro-)hunt.

I want to show a use case of how Elastic ELK can be used to "hunt" in order to find typo-squatting domains. Also, DNS was what got me into information security and I have been wanting to blog about the things I have been doing with Bro (DNS) and ELK for years.. but I never take the time...
So I will make this quick :)

Everyone loves ambulance chasers in infosec ;) so what better way than to write a quick blog regarding typo-squatting detection shortly after Brian Krebs' recent article:
https://krebsonsecurity.com/2018/04/dot-cm-typosquatting-sites-visited-12m-times-so-far-in-2018/

Elastic has a very powerful text/string analysis engine and with it you can perform queries that they refer to as "fuzzy" levenshtein distance. Therefore, lets look for some domains that have some form of character addition/substitution.
Lets look at some popular domains that are sometimes spoofed and then used in malware C2 comms -- for this example typo-squatting on google, microsoft, and only a few other domains (for the sake of brevity).
** Get creative and look for typo-squatting for your company :) bad folks love to use your companies/entities domain name for their C2. If you have to tune your search it will only take a few moments and then after that you could even turn your search into an alert. That gets sent via email(or other form of comms like slack/text) by using Elastic X-Pack Watcher OR something like elastalert. **

I have performed normalization on domain names that allow me to perform exact (match) queries on each level of a domain. for example "www.google.com". www = 3rd level, google = 2nd level, com = 1st level. The query for your environment may be instead "query:google~1".

Last visualization.. If you normalize DNS, HTTP, and SSL into a common schema then you can even perform one query to see all connections with a typo-squatting domain. Then you can quickly tell not only if a DNS lookup but an actual HTTP(s) connection. Also, you perform aggregations which is the other true power of elastic..
searching + aggregations = victory


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