Howto make IIS allow colon sign in request URL

I recently had Alfresco Community (4.2.f) behind an IIS reverse web proxy on port 80 (to hide /alfresco from outside access running on port 8080). The problem is that IIS by default does not allow request URLs containing colon (:) signs, and Share makes calls with unicode encoded : signs, in the form of %3a, for example as ”…type/cm%3afolder/formprocessor” when you create a folder in Share. IIS responds with error code 400 Bad Request for this type of call.

There are many confusing suggestions when you google this issue. You do NOT have to tamper with registry values as many suggest nor un-install security/Request Filtering from IIS.

Here’s how you solve this and make IIS accept requests containing colons, percentage signs, or any other forbidden character such as ampersand. Go to C:inetpubwwwroot (or wherever your web root might be) and open the file web.config. It probably contains the following:

You need to add a new section. Add the following at the top of the file, to allow colon sign but keep all other default invalid chars:

Note that I had to use the unicode encoded format of the invalid chars to make IIS accept the setting. Restart the IIS service (World Wide Web Publishing Service) and requests containing colon sign (as %3a) should now work fine.


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