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Advisory 25/2005: phpMyAdmin Variables Overwrite Vulnerability
From: Stefan Esser <sesser () hardened-php net>
Date: Wed, 7 Dec 2005 10:58:31 +0100

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                        Hardened-PHP Project
                        www.hardened-php.net

                      -= Security  Advisory =-



     Advisory: phpMyAdmin Variable Overwrite Vulnerability
 Release Date: 2005/12/07
Last Modified: 2005/12/07
       Author: Stefan Esser [sesser () hardened-php net]

  Application: phpMyAdmin 2.7.0(-rc1)
     Severity: A flaw in the variable overwrite protection may lead
               to several XSS and local and remote file inclusion 
               vulnerabilities
         Risk: Critical
Vendor Status: Vendor has released an updated version
   References: http://www.hardened-php.net/advisory_252005.110.html


Overview:

   Quote from www.phpmyadmin.net:
   "phpMyAdmin is a tool written in PHP intended to handle the 
   administration of MySQL over the Web. Currently it can create 
   and drop databases, create/drop/alter tables, delete/edit/add 
   fields, execute any SQL statement, manage keys on fields, manage 
   privileges,export data into various formats and is available 
   in 50 languages."
   
   A quick audit of the variable overwrite protection that was
   redesigned for phpMyAdmin 2.7.0 revealed an easy to exploit flaw,
   that leads to total failure of the protection and therefore 
   opens phpMyAdmin to a number of XSS, local and remote file
   inclusion vulnerabilities.


Details:

   phpMyAdmin comes with a register_globals emulation layer within
   grab_globals.php, to ensure compatibility with hosts where this 
   feature is turned off. This layer was heavily modified for the
   release of phpMyAdmin 2.7.0. One of the major changes is, that
   the blacklist of variables that may not be overwritten by the
   emulation layer is now stored in a global variable.
   
   Unfortunately the variablename $import_blacklist is not covered
   by the protection and therefore it was possible for an attacker
   to overwrite the blacklist. After the blacklist is overwritten
   an attacker can f.e. overwrite the $GLOBALS array with arbitrary
   content and therefore exploit several places where the $GLOBALS 
   array is used. 
   
   During normal execution this $GLOBALS array is just another way
   to access global variables, but when a script overwrites it,
   it becomes a normal variable, with a few exceptions in PHP4.
   For more information about what unexpected things can happen 
   when $GLOBALS is overwritten please have a look at
      
      http://www.hardened-php.net/globals-problem
   
   In phpMyAdmin $GLOBALS is used f.e. in the CSS generator to
   access the global variable that stores the configuration. Due
   to the fact, that the content of this variable is under total
   control of the attacker the path to an included file can be
   injected. This leads to an remote URL include vulnerability
   in PHP5 and a local file include vulnerability in PHP4.
   
   The difference is caused by the fact, that the PHP function 
   file_exists() does not work on URL wrappers within PHP4, but
   works on ftp:// URLs in PHP5. (When the host is running our
   Hardening-Patch for PHP such a remote URL inclusion is of 
   course not allowed and logged).
   
   Please also note that there are multiple (easy) ways to
   get PHP code into files on the server, so that local file
   inclusion vulnerabilities are more dangerous than they seem.
   Additionally it is possible to directly include PEAR.php
   from the installed PHP distribution. If it is one that
   was shipped with PHP <= 4.3.10 this can be used to directly
   execute code on the server by manipulating the destructor
   list.
   
   There are other places in phpMyAdmin, where this vulnerability
   can lead to XSS and other local file inclusion vulnerabilities.
   Those will not be listed separately, because the problem
   mentioned above is already serious enough to demonstrate the 
   impact of the failing overwrite protection.
         

Proof of Concept:

   The Hardened-PHP project is not going to release exploits for 
   this vulnerability to the public.


Disclosure Timeline:

   6. December 2005 - Disclosed vulnerability to vendor
   7. December 2005 - Release of new phpMyAdmin version
   7. December 2005 - Public Disclosure


Recommendation:

   It is strongly recommended to upgrade to the new version of
   phpMyAdmin which you can download at:

      http://www.phpmyadmin.net/home_page/downloads.php


GPG-Key:

   http://www.hardened-php.net/hardened-php-signature-key.asc

   pub  1024D/0A864AA1 2004-04-17 Hardened-PHP Signature Key
   Key fingerprint = 066F A6D0 E57E 9936 9082  7E52 4439 14CC 0A86 4AA1


Copyright 2005 Stefan Esser. All rights reserved.

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