Fiddler blocks Office 365 from authenticating

4 posts, 0 answers
  1. Mog0
    Mog0 avatar
    1 posts
    Member since:
    Jun 2018

    Posted 07 Jun 2018 Link to this post


    I've found that whenever fiddler is running on my PC (most of the time), Office 365 apps are unable to authenticate, for example, word can't access SharePoint 365 documents and OneNote can't sync notebooks stored on my OneDrive or on the SharePoint 365. They just keep prompting for my password. As soon as I close Fiddler, they authenticate and everything works again. Once authenticated, I can run Fiddler again and they keep working for a bit.

    Is there anything I can do to Fiddler's settings to get it to ignore Office 365 traffic?


  2. Alexander
    Alexander avatar
    383 posts

    Posted 13 Jun 2018 Link to this post


    Yes, you can. The proper way of doing this is to add Office 365 URLs which you want to be ignored as URLs for which Fiddler should be bypassed.

    In order to do that go to Tools -> Options -> Connections. You will find a text box with label "Bypass Fiddler for URLs that start with" in the bottom right corner. This is a semicolon delimited list of URLs (and the default <-loopback> token) and support * as a wildcard. Based on my testing it seems that you have to add "*", but I would suggest to confirm that this is the URL before adding it.

    Please, keep in mind that this textbox actually controls Windows WinINET settings (you can check them by Tools -> WinINET options) and in order to take effect you have to detach and reattach Fiddler (File -> Capture traffic or F12).

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  3. David
    David avatar
    1 posts
    Member since:
    Oct 2018

    Posted 24 Oct 2018 Link to this post

    What about if you're specifically *trying* to capture 0365 SAML traffic? I'm trying to do just that and experience the same issue with Internet Explorer. I want to be able to see the HTTP redirects and with Fiddler running, it prompts for credentials and fails. Can it be done?
  4. michael
    michael avatar
    1 posts
    Member since:
    Apr 2018

    Posted 29 Oct 2018 Link to this post

    Hi. I am getting the same issue monitoring O365 traffic for the entire day. It works fine whilst the access token is valid but the part where the refresh token needs to request new access token that is failing somehow as you just get 401 unathorized from that point onwards. Please help!



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