Some apps have no access to internet when Fiddler Classic is closed

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Fiddler Classic Windows
AJ
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AJ asked on 26 May 2023, 04:13 AM

I installed Fiddler Classic some time ago on recommendation from a friend for investigating an issue I was having which has since been resolved,. However I now have a problem where when I close (or even completely uninstall) Fiddler Classic, some apps on my PC (eg. Adobe Creative Cloud and Epic Games) can not access the internet. All other applications (eg. Chrome, Steam, Rambox, etc) still function perfectly fine. Even though this is the case, I have confirmed that the proxy settings are correct (ie. disabled) when Fiddler Classic is not running so I am not sure why this is occuring.

I no longer have a need for Fiddler Classic and I would like to remove it from my PC but this is obviously stopping me from being able to do so. Does anybody have any suggestion?

Rosen Vladimirov
Telerik team
commented on 26 May 2023, 11:26 AM

It is definitely strange and I assume some of those apps have their own settings for the proxy. So they've probably cached the Fiddler's proxy and try to send the traffic to it. Unfortunately, there's nothing Fiddler Classic can do to help in this case. As you've mentioned - the system proxy is no longer capturing traffic, but the applications already point to it. 
Maybe you can try starting Fiddler Classic, set the system proxy, then start the applications which have troubles. While they are working, stop Fiddler Classic from capturing, maybe the apps will detect the change and will stop using the proxy.
However, the best solution in this case is to contact the authors of those applications. They should be able to point you where are the cached settings of those apps which are still sending traffic to Fiddler Classic even when it does not act as system proxy (and especially when it is not running).
AJ
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commented on 26 May 2023, 11:38 AM

I've already tried what you have suggested including every iteration of starting/stopping/etc while the applications are open, before they're opened, after they're closed, etc., and including forcing those other applications to use other proxy servers to absolutely no avail. I'd expect, and almost guarantee, that any of those other software authors, when I explain the situation, would point me straight back here.

Rosen Vladimirov
Telerik team
commented on 26 May 2023, 11:42 AM

I understand and I'm trying to think what might cause the issue. One thing that comes to my mind - do those apps require startup as adminstrator? Maybe the settings are cached somewhere on the admin account and when you change the proxy settings, you change them only for your user.
AJ
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commented on 26 May 2023, 11:45 AM

I am logged in with the only account on the PC which is an administrator account. Also as an additional note, I have Fiddler Classic set to launch with capturing traffic disabled, so it's almost as if it is doing the opposite of what it seems like it should be doing.
AJ
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commented on 26 May 2023, 11:51 AM

Also they work whether or not Fiddler Classic is capturing traffic or not, as long as it is open.

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Nick Iliev
Telerik team
answered on 29 May 2023, 08:25 AM

Hello AJ,

 

By design, Fiddler Classic works as a WinHTTP and WinINET proxy (see the differences here). Enabling capturing tells Fiddler Classic to set itself as a system proxy, and all applications that are automatically respecting the system proxy will start going through it. However, even if Fiddler Classic is not acting as a system proxy, it still works as a proxy, so any application that is explicitly set to use the proxy address (by default, 127.0.0.1:8888) will successfully go through Fiddler. This is the expected code behavior of all intermediate proxies.

While some applications respect the dynamic change of the operating system proxy settings (which Fiddler sets/unsets when capturing is turned on/off), that is not true for all applications. For example, the Adobe Creative Cloud application seems to have issues when a WinHTTP proxy is dynamically set/unset (discussed here). In your case, it sounds like the Adobe application has "cached" the WinHTTP settings and still trying to use Fiddler as a proxy, even in cases where Fiddler Classis is already unset from the operating system.

To solve similar issues, you can try the following:

- Stop FIddler Classic and ensure the system proxy settings are unset successfully.

- Stop the third-party application (like Adobe Creative Cloud, Epic Launcher, etc.).

- Open a terminal and explicitly reset the WinHTTP proxy through the following command

netsh winhttp reset proxy

Alternatively, you can check whether the third-party applications are not explicitly set to use Fiddler as a proxy. For example, the Epic Launcher provides a Use Proxy setting (refer to the screenshot) that can cause the application to always look for a specific proxy address.


 

Regards,
Nick Iliev
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AJ
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commented on 29 May 2023, 12:05 PM

Hi Nick, that seems to have solved the issue, thank you.
Jaco
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commented on 06 Nov 2023, 06:00 PM

I solved this issue by opening cmd as administrator and typing the following

netsh winhttp reset proxy

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Nick Iliev
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