When I tried to install the certificate with this function, it popped up and installed the certificate, but still reminded me when I tried to decrypt the https traffic
"To view the encrypted sessions inside this tunnel, enable the Tools > Options > HTTPS > Decrypt HTTPS traffic option."

public static bool InstallCertificate()
        {
            if (!CertMaker.rootCertExists())
            {
                if (!CertMaker.createRootCert())
                    return false;

                if (!CertMaker.trustRootCert())
                    return false;
            }

            return true;
        }

Is it because of this function? What should I do, please help me...

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 and 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.
5. • 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

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

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

i used these settings:

public static void StartupFiddlerCore()
        {
            // Build startup settings:
            var settings = new FiddlerCoreStartupSettingsBuilder()
                                //.CaptureLocalhostTraffic()
                                .MonitorAllConnections()
                                .CaptureFTP()
                                .DecryptSSL()
                                .RegisterAsSystemProxy()
                                .OptimizeThreadPool()
                                .Build();
            FiddlerApplication.Startup(settings);
            //FiddlerApplication.oProxy.Attach();

        }

when i use WinSCP and use the fiddlerCore's ftp proxy to connect ftp server, the fiddlerCore's ftp proxy did net capture the ftp traffic.

the picture is winscp's proxy setting.

I am using fiddlerCore to capture ftp traffic, and i used the "CaptureFTP()" setting and "RegisterAsSystemProxy()" setting.

But when i use Winscp application with fiddlerCore's proxy to connect ftp server,it did not work,and connect failed. 

how dose fiddlerCore's ftp proxy work? how to use it?

Within a .net application when the CheckCertificateRevocationList is set SSL connections can no longer be made while fiddler is running.

An example:

ServicePointManager.CheckCertificateRevocationList = true;

WebRequest request = WebRequest.Create("https://www.google.com");

var response = await request.GetResponseAsync();

This fails with

The remote certificate is invalid according to the validation procedure.

If I register a validation callback (ServicePointManager.ServerCertificateValidationCallback) too  see what is going on I see

SSLPolicyErrors = RemoteCertificateChainErrors

When looking at the X509Chain I see "The revocation function was unable to check revocation for the certificate.\r\n"

Some other threads on stack overflow indicated this may be due to no revocation list being attached to the fiddler root certificates.

So I was wondering if anyone was able to get fiddler to work with the CheckCertificateRevocationList= true.  I know I can disable it but that would not be good for security. I also could in the handler allow fiddler certificates, but I was hoping there was a way to generate the fiddler certificates in a way that worked with that setting.

Hi,

I lost my data after recovering the data when I'm opening the saz file it shows me this error. "The selected file is not a Fiddler-generated .SAZ archive of Web Sessions."  Picture attached. A quick response will be highly appreciated 

Regards,
Raph

I need keep sending command FiddlerObject.utilIssueRequest(url);  and read result for stop command and stop working when the required result is achieved

example

stop1  if Body = 170 => send FiddlerObject.utilIssueRequest(url);

stop2  if Body = 170 => send FiddlerObject.utilIssueRequest(url);

stop3  if Body = 310 => send FiddlerObject.utilIssueRequest(url);

I have used FiddlerCore4.dll to capture the url. But I have the following problem that I don't understand why the error is.
I use fiddler capture request of a program. That program sends 2 urls. But the first url is captured by fiddler. The second url cannot be captured. I copied that 2nd url and pasted it in my web browser and fiddler caught it
Now how do I get the 2nd url from that software program to send?

I have sent a video of my test demo process. You can watch to understand the problem. At the same time, I have attached my 2 programs that I am testing in the video

Link Soft: https://drive.google.com/drive/folders/1nsDn71IQEsEw34Eev5BhdvqfrnrFpcSI

Link Video test: https://youtu.be/KaJ5UL2yq6w