BugTraq
BUG IN APACHE HTTPD SERVER (current version 2.0.47) Jan 31 2004 09:18PM
Vietnamese Security Group (security security com vn) (1 replies)


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 (at) yahoo (dot) com [email concealed]

http://www.security.com.vn

31 Nui Truc st. Ba Dinh dist. Ha Noi . Vietnamese

Phone : 84.4.8465701 / Fax: 84.4.8465701

[ reply ]
Re: BUG IN APACHE HTTPD SERVER (current version 2.0.47) Feb 03 2004 05:39AM
André Malo (nd perlig de)


 

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