From: SecuriTeam <support@securiteam.com.>
To: [email protected]
Date: 7 Jan 2007 20:13:28 +0200
Subject: [UNIX] WordPress Trackback Charset Decoding SQL Injection Vulnerability
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WordPress Trackback Charset Decoding SQL Injection Vulnerability
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SUMMARY
<http://www.wordpress.org>; WordPress was "born out of a desire for an
elegant, well-architectured personal publishing system built on PHP and
MySQL and licensed under the GPL. It is the official successor of
b2/cafelog. WordPress is fresh software, but its roots and development go
back to 2001. It is a mature and stable product. We hope by focusing on
user experience and web standards we can create a tool different from
anything else out there."
While testing WordPress it was discovered that WordPress supports
trackbacks in different charsets when PHP's mbstring extension is
installed. This feature can be abused to bypass WordPress's SQL parameter
escaping which leads to an SQL injection vulnerability that can result in
a compromise of the admin account and end in a server compromise.
DETAILS
Vulnerable Systems:
* WordPress version 2.0.5 and prior
Immune Systems:
* WordPress version 2.0.6
WordPress supports decoding trackbacks with different charsets when PHP's
mbstring extension is activated. Because the decoding happens after the
database escaping is performed choosing the right charset for the input
data allows bypassing the protection against SQL injection.
For the demonstration exploit that was shared with the WordPress
developers the UTF-7 charset was chosen, because it is the easiest to work
with. Other multibyte charsets that for example allow multibyte sequences
ending in '\' can also be used.
The exploit first checks if the mbstring extension is loaded by sending
only an UTF-7 encoded '0' in the title field. Because only a decoded '0'
will pass the empty() check this will trigger two different error
situations depending on mbstring availability.
The exploit continues with injecting bogus SQL commands into the SQL query
which will result in WordPress giving out detailed information about the
failed query. This error message is used to determine the configure
database table prefix, which is needed for the correct exploitation.
In the next step a harmless looking bogus comment is injected into the
comment table with a timestamp in the future. This is done to stop
WordPress from sending notification emails to the admin during the
password hash retrieval.
The rest of the exploit is a simple UNION SELECT injection that determines
password hashes by issuing a request for every bit of the hash (128 bits)
and checking which error message is returned. With the reconstructed
password hash it is possible to create a WordPress login cookie that can
be used to become admin.
As admin it is possible to edit (overwrite) all files within the blog
directory that are writeable. This can be used to inject arbitrary PHP
code in most installations. There exists a protection that denies loading
the wp-config.php file into the file editor, but it can be tricked by
directly sending a POST request that only saves the files. The
wp-config.php file is usually left writeable after the installation has
finished.
Disclosure Timeline:
29. December 2006 - Notified [email protected]
05. January 2007 - WordPress 2.0.6 release
05. January 2007 - Public Disclosure
Recommendation:
We strongly recommend to upgrade to WordPress 2.0.6 which also fixes
several other security vulnerabilities not covered by this advisory:
<http://wordpress.org/download/>; http://wordpress.org/download/
ADDITIONAL INFORMATION
The information has been provided by <mailto:sesser@hardened-php.net.>
Stefan Esser.
The original article can be found at:
<http://www.hardened-php.net/advisory_022007.141.html>;
http://www.hardened-php.net/advisory_022007.141.html
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