Fiddler no longer working after ie9 to ie11 upgrade

3 posts, 1 answers
  1. Ben
    Ben avatar
    2 posts
    Member since:
    Dec 2014

    Posted 07 Dec 2015 Link to this post

    ok, so some basic information to get out of the way:
    I'm in a corporate office that uses Group Policy to set settings. I am also NOT an administrator on my machine. Fiddler is, however, running elevated (or at least, it says it is)

    Prior to last week, I have had IE9 with Fiddler4 and been able to use fiddler without issue. The major change that has happened in the interim is that IE11 was pushed to my machine. as soon as that happened, I have been unable to use fiddler.
    I've done some tracking down with our Services team, and we found that our Anti-Virus/Malware/Spyware software is blocking Fiddler from making changes to proxy settings. We were able to validate this by first noticing a entry in the log of the Security software, but also by disabling the Security software and then run fiddler and it worked. The funny thing is, there have been no changes to the policy of the Security on the machines. The only change has been to move from IE9 to IE11. 
     So, I guess my question is this: I realize that since they are different versions, Fiddler will interact differently with ie9 and ie11, but was it really that big of a change to how it interacts that now the Security will catch it? We are just trying to understand this so that we can make smart changes to policies that can allow us to use Fiddler, but not be a large security hole.

     

    Thanks in advance.

  2. Answer
    Eric Lawrence
    Admin
    Eric Lawrence avatar
    833 posts

    Posted 07 Dec 2015 Link to this post

    Hello, Ben--

    Unfortunately, this isn't a Fiddler question, per-se. When it attaches as the system proxy, Fiddler asks the system to change the proxy settings to point to 127.0.0.1:8888 (where Fiddler listens). That request is sent to WinINET, the network stack that is used by Internet Explorer. It sounds like something is different between WinINET for IE9 and WinINET for IE11 such that the latter does something in such a way that your security software is unhappy.

    If Fiddler says it is running elevated, that means that either you are actually an administrator on your system, or your IT Admins have introduced some hackery whereby Fiddler runs elevated in some other user account.

    For what it's worth, if you're using Chrome or Firefox as your client, you can make either point to Fiddler without changing the system's proxy settings as a whole.

    Regards,
    Eric Lawrence
    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. Ben
    Ben avatar
    2 posts
    Member since:
    Dec 2014

    Posted 07 Dec 2015 in reply to Eric Lawrence Link to this post

    Thanks for the response Eric. 

     This is kind of what we were thinking (that Fiddler was doing the same thing in both cases) but just wanted to verify.  

Back to Top