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Bug: HTTP 403 (Forbidden) with FBA SharePoint Site

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We recently encountered a bug when trying to access a SharePoint site configured with Forms-Based Authentication from Internet Explorer.

The root site is restricted to authenticated users, whereas the /Public site is configured to allow anonymous users. In other words, when users attempt to browse to the root site (/), they should automatically be redirected to /Public/Pages/default.aspx (which contains a login form).

Everything was working great for awhile, but then we discovered that certain clients would encounter HTTP 403 (Forbidden) errors when attempting to browse to the root site before logging in. In other words, instead of redirecting to the /Public site as expected, IE would simply display the HTTP 403 error page (which, at first glance, actually makes it seem like the site is down).

We observed the site worked just fine from the same clients when using Firefox, and it only occurred on a couple of laptops when using IE8.

We also noticed that we could workaround the problem by explicitly browsing to the /Public site instead of relying on the redirect -- hence we "punted" the issue for a short period, hoping that the issue could only be reproduced on our Microsoft laptops.

At first we suspected the problem was due to specific IE options, but resetting the IE configuration didn't resolve the issue.

Next, we suspected a specific version of IE8, since we noticed it happened on Windows 7 but not on Windows Server 2008.

However, then we discovered that it worked on one laptop but not another -- even though both laptops were running Windows 7 (x64) and had the exact same version of Internet Explorer.

Fortunately, Ranjiv Sharma -- one of my colleagues on the project -- discovered the following blog post:

403 Forbidden and Forms Authentication with MOSS. 2009-05-21.

https://vettekerry.wordpress.com/2009/05/21/403-forbidden-and-forms-authentication-with-moss/

It turns out the problem is caused by the Microsoft Office Live Add-in 1.3. Once you remove the add-in, close all instances of Internet Explorer, and restart IE, the seamless redirect works as expected.

Update (2010-01-15)

This is a known bug:

You cannot view a forms-based authentication Windows SharePoint Services 3.0 site if you have Office Live Update 1.2 for Microsoft Office Live Workspace installed
https://support.microsoft.com/kb/972535

According to the KB article, it is fixed in the June 2009 Cumulative Update (CU). From my experience, it also appears to be fixed by installing the 1.4 of the Microsoft Office Live Add-in.

Note that I tried reinstalling the Office Live Add-in on my VM to try to repro the error again prior to installing the June 2009 CU. Unfortunately, I couldn’t find the 1.3 version available for download anymore from microsoft.com (the download page is no longer available). When I downloaded and installed the 1.4 version, I was unable to repro the error when browsing locally from my VM.

I subsequently downloaded the June 2009 CU and proceeded to install it on my local VM (since I could still test with the 1.3 version of the Office Live Add-in from my laptop). Unfortunately, I could only install the WSS part of this CU – not the MOSS part. (The MOSS patch is giving me the dreaded “expected version of the product was not found on the system” error.)

However, even with just the WSS portion of the June 2009 CU, I am no longer seeing the error when browsing to my local VM from my laptop.

Comments

  • Anonymous
    March 08, 2010
    Just to say that we have built a Sharepoint 2007 server using the latest updates and we still have clients encountering the same problem. Specifically anyone with Windows 7 and IE8, (and any version of Office Live addin-in eg 1.4). The only fix we have found is to uninstall Office Live Add-in. Or to switch your browser to Google Chrome, Firefox.

  • Anonymous
    March 10, 2010
    If you've installed the June 2009 Cumulative Updates for SharePoint on your server(s) and you still experience the problem, I strongly encourage you to open a support case with Microsoft. Since this is a bug that is reportedly fixed in that CU, the support case shouldn't cost you anything (in other words, it should be a non-decrementing SRX).