Applications Bypassing Fiddler 4 Proxy

[Alan]

Running Fiddler v5.0.20194.41348 on Windows 7 and trying to debug a login process with AqBanking (part of gnucash). AqBanking is bypassing the Fiddler proxy. Actually quite a few applications are bypassing Fiddler. The Fiddler proxy is showing active any time capture is enabled (127.0.0.1:8888 active for HTTP and Secure). Other applications have no network config options, but they do use the Windows TCP/IP stack. Firefox, Chrome, and MSIE are all functioning with Fiddler 4 active.

How do I force ALL Windows network applications to work with Fiddler?

[Simeon]

Hi Alan,

Fiddler is a proxy and as such it always listens on some port (8888 by default). Here is a blogpost explaining how Fiddler works as a proxy.

How do I force ALL Windows network applications to work with Fiddler?

Unfortunately, there is no straightforward way to force all apps to work with Fiddler. The problem is that each application implements its own proxy settings. Some of these implementations like MSIE, Chrome, Firefox if configured, etc. are aware of the WinINET proxy settings and use them. When Fiddler "attaches", it changes the WinINET proxy settings to point to 127.0.0.1:8888 (where Fiddler is listening) and all applications which use these proxy settings will start to send their HTTP/S traffic to Fiddler. There are also many applications which are implemented in such a way to not use the WinINET proxy settings. Maybe they are using the WinHTTP proxy settings or have their own proxy settings or don't have proxy settings at all.

I am not familiar with the AqBanking app but basically you have to find out how to modify its proxy settings and change them to 127.0.0.1:8888

Regards,
Simeon
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