Internet Explorer 11 cannot connect to local host – Redux

Updated 11 November 2013

In a previous blog post, I detailed how Internet Explorer 11 for Windows 8.1 Preview fails to open http://127.0.0.1 while it has no problems opening http://localhost, given an appropriate web server is installed. Well, here is an update.

Screenshot - 1. IE11 cannot connect to 127.0.0.1

In the original post, I wrote:

I tried tweaking Internet Explorer’s enhanced protection settings to work around this issue but it was all in vain. I still think Microsoft, I or both might have missed something there. I strongly believe it should have had some effect.

I tried my luck with Internet Explore 11.0.9600 for Windows 8.1 RTM. Disabling either Protected Mode or Enhanced Protected Mode indeed enables access to http://127.0.0.1., both in desktop version and Metro-style version.

Now, perhaps I should elaborate a little bit about the difference between Protected Mode and Enhanced Protected Mode.

Protected Mode is added in IE7 and can be disabled on a per-zone basis, from Security tab of Internet Options dialog box. In fact, starting with Internet Explorer 8, Protected Mode is by default disabled for local intranet zone. So, if you add 127.0.0.1 to the local intranet zone or trusted zone, you can access it with Internet Explorer. For more information, see:

Enhanced Protected Mode is added in IE10 and can only be disabled via Advanced tab of Internet Options dialog box. Disabling or enabling it requires a system restart. It causes a lot of compatibility issues with plug-ins but Microsoft is generally not in good terms with plug-ins. For more information, see:

Is this still a bug?

Short answer: Yes. There is no security-conscious justification for letting any piece of software treat 127.0.0.1 and localhost differently. Both go to the same place and are authenticated equally. (Mind you, the are reasons for treating, say, 64.4.11.42 and http://www.microsoft.com differently, but that’s not the case here.)

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Posted on 9 November 2013, in Software Development, Software Review and tagged , , , , , , , , , , , , , , . Bookmark the permalink. 1 Comment.

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