As noted in the Fiddler book,

Sessions rerouted from one hostname to another using the Host Remapping tool are rendered with a light blue background in the Web Sessions list. HTTPS Sessions that have been rerouted have the X-IgnoreCertCNMismatch and X-OverrideCertCN Session Flags set to avoid raising “Certificate Name Mismatch” errors.

However, there's a bug. In the HostsFile.cs code, there's are several places that look like:

            if (oS.isTunnel) {

                oS["x-overrideCertCN"] = oS.hostname;
                oS["X-IgnoreCertCNMismatch"] = "HOSTS-Ext";
            }

This usually works for browser traffic going through Fiddler (because the HTTPS handshake is typically conducted on the CONNECT tunnel). However, it doesn't work (and the user is spammed with cert error warnings) if the traffic is sent from Fiddler itself (e.g. via Composer or using the "Reissue requests" context menu item). 

The code should look like this:

            if (oS.isHTTPS || oS.isTunnel) {

                oS["x-overrideCertCN"] = oS.hostname;
                oS["X-IgnoreCertCNMismatch"] = "HOSTS-Ext";

           }

I was using Fiddler, working with AutoResponder, and hit an object reference not set error. I didn't notice anything obvious not working after dismissing the error.

I don't have exact repro steps, but thought I would pass along the stack trace.

 

---------------------------
Uncaught Exception in Session #118
---------------------------
Fiddler has encountered an unexpected problem. If you believe this is a bug in Fiddler, please copy this message by hitting CTRL+C, and submit a bug report at http://www.telerik.com/forums/fiddler.

Object reference not set to an instance of an object.

Type: System.NullReferenceException
Source: Fiddler
   at Fiddler.AutoResponder.(Session , ResponderRule ) in C:\Jenkins\Fiddler_Windows\workspace\FiddlerCore\FiddlerCore.Shared\Common\AutoResponder.cs:line 1787

   at Fiddler.AutoResponder.(Session ) in C:\Jenkins\Fiddler_Windows\workspace\FiddlerCore\FiddlerCore.Shared\Common\AutoResponder.cs:line 2026

   at Fiddler.Session.() in C:\Jenkins\Fiddler_Windows\workspace\FiddlerCore\FiddlerCore.Shared\Common\Core\Session.cs:line 5414

   at Fiddler.Session.‘() in C:\Jenkins\Fiddler_Windows\workspace\FiddlerCore\FiddlerCore.Shared\Common\Core\Session.cs:line 3628

   at Fiddler.Session.(Object ) in C:\Jenkins\Fiddler_Windows\workspace\FiddlerCore\FiddlerCore.Shared\Common\Core\Session.cs:line 3522


Fiddler v5.0.20202.18177 (x64 AMD64) [.NET 4.0.30319.42000 on Microsoft Windows NT 6.1.7601 Service Pack 1] 
---------------------------
OK   
---------------------------

Hello, we have found the issue on the v5.0.20202.18177 for .NET 4.6.1 the session data could be copied only using hot keys.

ctrl+shift+s

but only session url is saved when I try to Copy session by clicking on the menu item.