Option to make Fiddler respect browser's DNS-over-HTTPS (DoH)?

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Noob Saibot
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Noob Saibot asked on 21 Oct 2022, 05:55 PM

I know that Fiddler uses local DNS resolver as it didn't work on some test sites that only worked through DoH geobypassing proxy. Are there any trick/method to make Fiddler respect browsers DoH setting? If not, would you guys please consider adding it since DoH/DoT seems to be very useful/popular these days.

Here's some use case scenarios

  • You want to hide your DNS queries from your ISP while doing Fiddler session on a browser.
  • Your ISP filters your DNS (transparent DNS proxy, etc) and you want to debug sites that are blocked by your ISP with Fiddler.
  • You want to debug geo-blocked sites which can be bypassed by geo-bypassing DoH resolver.
  • and so on.

You can also add following to any of the scenarios above if we think alternative solutions like using Windows 10/11, configuring DoH on the router, using VPN, etc.

  • "you use an operating system that doesn't support configuring DoH/DoT"
  • "your ISP/Organization blocks VPN/proxies"
  • "your router doesn't support DoH/DoT"

BTW, I know Microsoft natively added DoH in Windows 10 more than a year ago, DoT to Windows 11 insider build a few months ago. I don't know if Fiddler works on them (works as in properly using DoH/DoT) as i don't use those OSes. I am curious to know about it though.

Anyways,

Here's quick guide to confirm that Fiddler/Firefox bypasses DNS-over-HTTPS just in case anyone wants to test.

Open Firefox (Use this guide for other browsers)

  1. Click the menu button Fx89menuButtonand select Settings.
  2. In the General panel, scroll down to Network Settings and click the Settings… button
  3. Check "Use system proxy settings"
  4. Scroll down to Enable DNS over HTTPS.
    • On: Select the Enable DNS over HTTPS checkbox.
      Check Custom and paste this server (this is DoH DNS resolver that blocks social media sites we are using for the test)
    • https://freedns.controld.com/p3
    • Press OK

  5. Open www.facebook.com and it should be blocked.

  6. Now open Fiddler and try to open www.facebook.com again on the browser. Facebook will work.



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Nick Iliev
Telerik team
answered on 24 Oct 2022, 10:51 AM

Hi Shang Tsung,

 

While there is no out-of-the-box Fiddler support for DNS-over-HTTPS set through the browser settings, Fiddler works as a system proxy and will respect any settings applied in the operating system network configuration. One possible solution is to set your DOH in Windows network settings instead - see the link below for instructions on how to set DOH on Windows 11.

https://winbuzzer.com/2022/01/19/how-to-enable-dns-over-https-doh-on-windows-11-xcxwbt/

 

 

Regards,
Nick Iliev
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Noob Saibot
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commented on 30 Oct 2022, 05:02 AM

Yeah. I actually mentioned alternative solutions in my post above and i am currently in the following scenario.

  • "you use an operating system that doesn't support configuring DoH/DoT"

But no big deal though as i can set DoH on my router. Just thought it's something nice to add to Fiddler if it's doable.

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Nick Iliev
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