Advisory 25/2005: phpMyAdmin Variables Overwrite Vulnerability



-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


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.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: For info see http://www.gnupg.org

iD8DBQFDlrwQRDkUzAqGSqERAmRXAJ91rK7yBmaD11xKZYT/3AQssLcx1ACdEmxV
ikwFLy/0HqQmcWp98DVzCVk=
=BCKL
-----END PGP SIGNATURE-----
© Hardened PHP Project