dns wildcard blocking


Author: David Zimmer
Date: 11.03.17 - 5:39pm



for years I wished the windows hosts file supported dns wildcard matching so I could block things on pretty wide filters.

I have been playing around with a Win10 machine and watching the traffic it generates. Live tile requests, windows update requests, data and services, telemetry, and god knows what else..

This annoys me on two fronts. One the machine is out of my control and it is doing things I cant know. Two if I want to capture traffic, now it is bulked up with loads of irrelevant crap I have to wade through. So the desire for wildcard dns blocking grew.

Yesterday I finally found a cool library that let me implement it in about 3 hrs.

The Windivert library by Basil is an easy to use kernel driver that lets you intercept, drop, relay, and modify raw packets. It supports Vista+ machines and has a good set of python bindings already made for it.

This is the same library that the FireEye FakeNet-NG project designed by Peter Kacherginsky uses to record and redirect traffic for malware analysis.

Ripping some code from FakeNet and browsing online pydivert examples I was able to throw together a quick sample that fit my specs.

Just double click on dnsblock.py and it will intercept and log all dns requests. You can white or black list domains and/or processes in config.txt. Anything blocked just gets resolved to localhost.

Its small, its python, and its easy to modify. Use pip to install pydivert and dnslib.

Notes:
  • it doesnt do anything against direct ip connections.
  • you may want to delete the dnscache service from registry and reboot (make sure to export and back it up first!) otherwise most requests coming from system services will always be routed though the dnscache service and you wont be able to see the actual requestor.

Good first step and also nice easy way to monitor all dns requests and easily block them.

DNSBlock Github repo




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