HOWTO: OpenWRT and Fiddler for HTTP and HTTPS Transparent Proxy traffic capture – Part 2

Goal:

• Setup a Hyper-V test lab for capturing traffic from an Android client.
• Use OpenWRT as the routing gateway for the private VM network and Transparent Proxy HTTP and HTTPS traffic to Fiddler.
• Config Fidder for traffic capture.

See Also:

• Part 1 – Building OpenWRT image for Hyper-V
• http://www.telerik.com/forums/fiddlercore-as-transparent-proxy

Configuring OpenWRT for Transpart Proxy

• Create Port Forward / Pre-routing rules for TCP port 80 and 443 to forward traffic to Fiddler.
  • Assuming Fiddler is running at 192.168.1.2, port 8888 for HTTP proxy and 8443 for HTTPS proxy.
  • Exclude the Fiddler machine from the port forward.

  
  

• Create Source NAT / Post-routing rule

  
  

   

• OR write the rules in the Firewall Custom Rules page.

  
  

   

Configuring Fiddler for Transpart Proxy

• Enable “Allow remote computers to connect” in Fiddler Options and open corresponding ports in the Windows Firewall.

  
  

• Use the command “!listen 8443 your_dummy_CN” to make Fiddler to listen to port 8443 for HTTPS proxy.
  • The dummy CN value is important. Without the CN value Fiddler will not handle the HTTPS handshake.

  
  

• Use the command “prefs set fiddler.network.https.SetCNFromSNI true” to make Fiddler to generate the cert with CN to match the incoming request.

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