Q: Fiddler Interrupts WebEx traffic

[EricLaw]

Several users have noted that the WebEx client fails to connect while Fiddler is running.

The problem is that WebEx traffic is not actually valid HTTPS traffic (it is using HTTPS simply as a tunnel for RPC traffic), and as a consequence Fiddler stalls waiting for valid HTTP requests on the connections. WebEx's invalid requests are never completed and thus the traffic stalls before timing out. Fiddler has special code to resolve this situation for Microsoft Outlook/Exchange's "RPC-over-HTTPS" feature, but the WebEx traffic does not use the HTTP Methods used by RPC-over-HTTPS and thus does not benefit from that work.

The easiest workaround for this issue is to simply exempt the WebEx connections from decryption, which means that their traffic will flow silently through Fiddler.

To do so, click Tools > Fiddler Options > HTTPS. In the "Skip decryption for the following hosts" box, add *.webex.com and click Ok.

Alternatively, inside Rules > Customize Rules > OnBeforeRequest, you can do

  var sProc = oSession["X-ProcessInfo"];

  if (!String.IsNullOrEmpty(sProc) && sProc.StartsWith("atmgr"))

  {

    oSession["x-no-decrypt"] = "FiddlerScript says atmgr process should not decrypt";

  }