Do not trust HOST header

Posted:   |  More posts about apache http security

This is nasty and definitely unexpected. While reading through the article, I still have a feeling that this is not possible (at least on ubuntu) since default install of apache always create a default vhost that can act as catch-all handler in case user pass nonsense Host header but this paragraph opened my eye:-

However, the arguably ultimate authority on virtual hosting, RFC2616, has the following to say:

5.2 The Resource Identified by a Request [...] If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request MUST be ignored. The result? On Apache and Nginx (and all compliant servers) it's possible to route requests with arbitrary host headers to any application present by using an absolute URI: POST HTTP/1.1 Host:

For so long I think HOST header is the definitive source to determine which site to serve under virtual hosting. A quick test proved this newly found fact:-

echo -en "GET /password-reset/ HTTP/1.1\r\nHost:\r\n\r\n" | nc 80
HTTP/1.1 200 OK
Date: Wed, 25 Sep 2013 07:54:00 GMT
Server: Apache/2.2.22 (Ubuntu)
Last-Modified: Fri, 13 Sep 2013 08:07:54 GMT
ETag: "25a9c-b1-4e63f5a01c982"
Accept-Ranges: bytes
Content-Length: 177
Vary: Accept-Encoding
Content-Type: text/html
X-Pad: avoid browser bug

<html><body><h1>It works!</h1>
<p>This is the default web page for this server.</p>
<p>The web server software is running but no content has been added, yet.</p>

So we still safe, apache serve the default vhost. But this one:-

echo -en "GET HTTP/1.1\r\nHost:\r\n\r\n" | nc 80

Give you the page of ! Fortunately Django 1.5 has fixed for this. Better check if your app depend on the HOST header to build absolute url.

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