Adding case-insensitive regex

[Fox0x01]

During a test I had an issue with an DNS resolver of my target host malforming the DNS queries (uppercase/lowercase). Beause of this, the dnscat2 server was unable to establish a session. I fixed this issue by adding case-insensitive regex modifiers (/i).

[iagox86]

Interesting! Was it making the domain uppercase or were you trying to use a domain with case?

I noticed that OS X mangles case in its resolver, which is why I started using all lowercase (I originally used base64). It didn't occur to me to make the regexes case insensitive, that's a good idea!

[Fox0x01]

I captured the packets with tcpdump and noticed the DNS queries being a mix of upper and lower case characters. For example: Foo.ExamplE.net.
Found an article about this behavior: https://developers.google.com/speed/public-dns/docs/security?hl=en#randomize_case

It seems that this is a "security" technique to add entropy to requests by randomizing case in query names.

[iagox86]

Thanks for the info! In addition to merging your diff, I also called out the behaviour in the docs:

d8bb539

Let me know (or send another pull request) if you want to be credited a different way :)

[Fox0x01]

Thank you! :)