bugtraq - Re: BUG IN APACHE HTTPD SERVER (current version 2.0.47)

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Date: 3 Feb 2004 13:48:53 -0000
From: Vietnamese Security Group <security@...urity.com.vn>
To: bugtraq@...urityfocus.com
Subject: Re: BUG IN APACHE HTTPD SERVER (current version 2.0.47)


In-Reply-To: <20040131211851.30391.qmail@....securityfocus.com>

Note : of course it affected also in the current version 2.0.48 ( tested) 

Vietnamese Security Group
www.security.com.vn


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>From: Vietnamese Security Group <security@...urity.com.vn>
>To: bugtraq@...urityfocus.com
>Subject: BUG IN APACHE HTTPD SERVER (current version 2.0.47)
>
>
>
>APACHE HTTPD SERVER (current version 2.0.47):
>##########################################################
>How to return files in a Apache Deny All directory.
>The Directives controlling host access may be bypassed even 
>if they have not permission to be override.
>
>11 Jan 2004
>
>
>DESCRIPTION
>
>Apache Web Server allows manage configurations via the main 
>httpd.conf file, and via the other configuration files placed 
>inside the children web trees, may owned by the user accounts, 
>named .htaccess by default. The server administrator further 
>controls what Directives may be placed in .htaccess files by 
>configuring the AllowOverride Directive in the main httpd.conf 
>files.
>
>If the server admin sets the Deny Directive to All (for example), 
>and does not allow the user accounts to modify this Directive in 
>their .htaccess file by setting the AllowOverride values without 
>the Limit type, his/her users are still able to bypass the Deny 
>option by using the ErrorDocument Directive.
>
>Tested in Apache 2.0.47/RH-Linux/WinXP.
>
>
>EXAMPLE
>
>##########################################################
># In the main httpd.conf file:
>#
><Directory />
>    AllowOverride FileInfo
>    Deny From All
></Directory> 
>##########################################################
>
>##########################################################
># In the user's .htaccess file placed in a child directory:
> 
>ErrorDocument 403 /child/dir/fetch.php
>
>##########################################################
>
>/********************************************************/
><?php
>// In the fetch.php placed in the same directory:
>
>$url = parse_url( $_SERVER['REQUEST_URI'] );
>@include basename( $url['path'] );
> 
>?>
>/********************************************************/
>
>
>In this example, assuming the web server can execute PHP script 
>or some scripts/server-includes. By modifying some codes you can 
>return other mime file types such as image/gif etc.
>
>Event if the server does not allow any file parsed (Deny From All), 
>the script file fetch.php will still be executed, and it includes 
>again and parses any other files in a same directory, which 
>indecated by the query variables, to the web client. 
>
>Looking in the source code, I think the missing auth checking is in 
>the function ap_process_request_internal() in the file request.c. 
>One of the major changes in Apache 2.0 is to the internal redirect 
>mechanism. To prevent the code from falling out of sync again in the
>current directory, the configuration comparing between two config 
>directories may bypass the authentication checking again. That 
>explains why this vulnerability (if any?) can only done if the 
>redirect ErrorDocument file is placed in the same request directory.
>
>
>
>FIX
>
>Do not skip auth checker even if the per_dir_config member value 
>doesn't change in the ap_process_request_internal() function.
>
>
>NOTE 
>
>I post this issue in the public mailing list, because I think this 
>vuln is not exploitable by a remote attacker. If something were 
>wrong, drop a line to me.
>
>
>Vietnamese Security Group
>Trung - caothuvolam - trungonly@...oo.com
>http://www.security.com.vn
>
>31 Nui Truc st. Ba Dinh dist. Ha Noi . Vietnamese
>Phone : 84.4.8465701 / Fax: 84.4.8465701
>