Unable to redirect https traffic from external IP to loopback interface in Fiddler

Question

I'm trying to use Fiddler to capture traffic that comes to my machine on its external ip address, and redirect it to the loopback interface without affecting the host header.

I have added the following to the OnBeforeRequest method:

if (oSession.HostnameIs("MyMachineName")){
   oSession.bypassGateway = true;                 
   oSession["x-overrideHost"] = "localhost";
}

This works fine for http traffic: I do indeed see a request to http://MyMachineName hit the loopback adaptor with its host header intact.

However, when intercepting https traffic I get the following in the response raw view:

fiddler.network.https> HTTPS handshake to auth.time-wise.net failed. System.IO.IOException The handshake failed due to an unexpected packet format.

I have Fiddler configured to capture and decrypt https traffic.

Does anyone know why this problem occurs and how it can be remedied?

Edit: in response to Eric's request for more information

Fiddler is running as a proxy (i.e. as standard), listening on port 8888. The clients are (currently) web browsers on the same machine, and so are automatically using the Fiddler proxy, as they've picked up the change in default proxy.

EricLaw EricLaw · Accepted Answer · 2014-08-14T21:01:49

You've left out some important details (e.g. what port is Fiddler running on, and how did you configure the remote client to send its traffic to Fiddler?)

Having said that, you will probably want to change your use of x-overrideHost to x-overrideHostname such that the port number of the traffic being retargeted is preserved.

Unable to redirect https traffic from external IP to loopback interface in Fiddler

1 Answers