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I think what I was asking for was a bit hard to understand, so, I am trying to make it simpler...

I need my server to have a custom 400 error page when it receives a request with a malformed host header.

What I ideally want is ErrorDocument 400 \somepage.php

I can generate 400 errors by visiting a page such as http:\\myserver\bla%bla, and this will go to my script fine. Likewise, I can change the \somepage.php section to Test text and Apache will return that text.

If however, the 400 error is due to a malformed host header, it will work with the text but not the web page.

Can anyone shed any light on this and give a working solution before I loose all my hair?! (already lost quite a bit over this!).

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What exactly does the error log say ? Have you correlated it with the access logs ? Do a TCP dump of the traffic, and show what is really sent over the wire. We need more information to be able to help. – adaptr Mar 8 '12 at 9:47
Yes I have... I thought that was enough information that I gave - the request has invalid headers and Apache returns in the error log - "Client sent malformed Host header", along with a standard 400 error in the access.log .... And again, a string gets returned.... just not a page... If you do need more information, I am happy to give it, but, I am not sure it is needed... I am almost certain the error is just that it can't locate the custom error, I just can't figure out how to actually process it! – William Hilsum Mar 8 '12 at 11:21
up vote 1 down vote accepted

After trying many things, it turns out that this isn't possible.

I opened a ticket on HTTPD's Bug Tracker - which was closed with Won't Fix.

They say that:

Marking as wontfix, when a request is malformed, the server isn't willing to do further processing to serve a custom errordocument out of the filesystem (your error page should have told you a recursive 400 was encountered)

In my opinion, this isn't very good - I understand this being the default action, but, why not let a user use a different page if they so wish.

Quite frankly, it should work this way, but, if anyone comes up with an answer that involves any other technique (proxy, rewrite/similar), I will be happy to look at it and possibly give that the answer mark.


In the end, I found out that it is possible to do this with Nginx and a custom directive to redirect 400 pages. I do not understand why Apache Devs won't acknowledge this, but, Nginx did it fine.

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