phpGB: DoS and executing_arbitrary_commands

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ppp-design found the following design error in phpGB:

Details

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Product: phpGB
Affected Version: 1.20 and maybe all versions before
Immune Version: 1.30
OS affected: all OS with php
Vendor-URL: http://www.walzl.net
Vendor-Status: informed, new version avaiable
Security-Risk: high - very high
Remote-Exploit: Yes

Introduction

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phpGB ist a php/mysql based guestbook. Admin can change all settings
within a php interface. Unfortunately the script lacks correct
authentification, so everybody is able to override a config file,
which leads to a DoS or to running arbitrary php commands on the server.

More details

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The problem is in /admins/savesettings.php. The only check for
authentification is made is a check for the page being requested via
POST. That is why it is very easy to fake authentification and to
write anything to /include/config.php. Because this is a major file of
the software being included nearly on every page, a syntax error
leads to a DoS of the whole guestbook. One more security aspect is
the ability to insert arbitrary commands in the config file. When
avoiding syntax errors, a possible blackhat is able to execute any
php command on the server.

Proof-of-concept

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After running the following proof of concept, you are presented with
phpinfo() on every page of the guestbook. Of course you can insert any
php code instead of phpinfo(); into /include/config.php. (\n is newline)

telnet example.com 80\n
POST /phpGB/admin/savesettings.php HTTP/1.0\n
Content-Type: application/x-www-form-urlencoded\n
Content-Length: 123\n
dbpassword=%22%3Bphpinfo%28%29%3B%24a%3D%22&toolbar=1
&messenger=1&smileys=1&title=1&db_session_handler=0
&all_in_one=0&test=\n
\n

Temporary-fix

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Use .htaccess to restrict access to admin pages.

Fix

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Use at least phpGB 1.30.

Security-Risk

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Because a attacker is able to execute any php command, he is able to
read all files including .htaccess or .htpasswd files or any password
protected pages. Depending on system security he might be able to run
any shell command on the server. That is why we are rating this
security issue to high - very high.

Vendor status

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After we have informed the author he needed about 12 hours for a new
version.

Disclaimer

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All information that can be found in this advisory is believed to be
true, but maybe it isn't. ppp-design can not be held responsible for
the use or missuse of this information. Redistribution of this text is
only permitted if the text has not been altered and the original
author ppp-design (http://www.ppp-design.de) is mentioned.

This advisory can be found online:
http://www.ppp-design.de/advisories.php

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ppp-design
http://www.ppp-design.de
Public-Key: http://www.ppp-design.de/pgp/ppp-design.asc
Fingerprint: 5B02 0AD7 A176 3A4F CE22 745D 0D78 7B60 B3B5 451A
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