Fiddler does not work with corporate proxy - cannot chain to upstream gateway

3 posts, 1 answers
  1. Dan
    Dan avatar
    2 posts
    Member since:
    Sep 2019

    Posted 05 Sep 2019 Link to this post


    since my company brought in a new corporate proxy (IBoss) I am unable to use Fiddler.

    Any ideas please? The error I receive is "The system proxy was changed. Click to reenable Telerik Fiddler capture".

    From some googling I am guessing that IBoss proxy is changing settings as soon as Fiddler makes a change.

    In IE, I do not have any entries in Internet Options -> LAN Settings -> Proxy Settings (and these settings are now blank & disabled).  There is an automatic config script.

    If I use foxy proxy to change proxy to localhost and give a port, I can capture local traffic but nothing external (ie anything that should go though IBoss). Have tried several Gateway options in Fiddler but unsure what Fiddler needs.

    Any thoughts please?




  2. Answer
    Eric R | Senior Technical Support Engineer
    Eric R | Senior Technical Support Engineer avatar
    388 posts

    Posted 05 Sep 2019 Link to this post

    Hi Dan,

    From my limited understanding, iBoss a comprehensive cloud Firewall/Gateway and has the capability to set user and group policies. It could be that they System Proxy Settings are being controlled by iBoss. If that is the case, the settings would need to be configured in iBoss.

    With that said, it may be possible to configure the System Proxy to use the Automatic Config Script and then run Fiddler with the Use System Proxy setting. See the below screenshot for an example.

    Please give this a try and let me know the results. Thank you and I look forward to your reply.


    Eric R | Technical Support Engineer
    Progress Telerik

    Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal and vote to affect the priority of the items
  3. Dan
    Dan avatar
    2 posts
    Member since:
    Sep 2019

    Posted 09 Sep 2019 in reply to Eric R | Senior Technical Support Engineer Link to this post

    Hi Eric

    thank you for the suggestion. After a bit more experimentation I now have both internal AND external sites capturing :)

    I am still seeing the warning that 'System proxy was changed' but as all transactions appear to be captured, I will just ignore that for now!

    The 'Automatically detect settings' option you screenshotted is greyed out for me, but iBoss runs a service anyway, which perhaps overrides any of the browser settings.

    The settings 'Use setup script' and 'Script Address' are set to On and populated with the pac file. I confirmed that the .pac file is accessed by viewing result of Options -> Connections tab (by looking at 'Copy BrowserProxy Configuration URL). Then set Fiddler using 'Use System Proxy' under Options -> Gateway tab.

    For my particular case, I am running foxyproxy in order to quickly move between different settings - I think this might be the key to this working in my environment, since I would be unable to set a port or host otherwise.

    Many thanks


Back to Top