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SektionEins GmbH
www.sektioneins.de
-= Security Advisory =-
Advisory: PHP ZipArchive::extractTo() Directory Traversal Vulnerability
Release Date: 2008/12/04
Last Modified: 2008/12/04
Author: Stefan Esser [stefan.esser[at]sektioneins.de]
Application: PHP 5 <= 5.2.6
Severity: PHP applications using ZipArchive::extractTo() to unpack zip
archive files can be tricked to overwrite arbitrary files
writable by the webserver which might result in PHP remote
code execution
Risk: Medium
Vendor Status: Vendor has released PHP 5.2.7 which contains an updated
ZipArchive::extractTo() method that flattens the filename
stored inside zip archives before unpacking
Reference: http://www.sektioneins.de/advisories/SE-2008-06.txt
Overview:
Quote from http://www.php.net
"PHP is a widely-used general-purpose scripting language that
is especially suited for Web development and can be embedded
into HTML."
PHP comes with the zip extension that provides the ZipArchive
class for zip archive manipulation. During an audit of a large
scale PHP applications that uses ZipArchive::extractTo() to
unpack user uploaded zip archives to temporary directories it
was discovered that ZipArchive::extractTo() does not flatten
the filenames stored inside the zip archives.
Therefore it is possible to create zip archives containing
relative filenames that when unpacked will create or overwrite
files outside of the temporary directory.
In the applications like the one in question this results in
a remote PHP code execution vulnerability, because we are
able to drop new PHP files in writable directories within
the webserver's document root directory.
Details:
No details required. To exploit this an attacker just needs to
create a zip archive containing filenames like
../../../../../../../../../../../var/www/wr_dir/evil.php
An easy way to achieve that is to just store a file with a long
name inside the zip archive and then change it with a hex editor
Proof of Concept:
SektionEins GmbH is not going to release a proof of concept
exploit for this vulnerability.
Disclosure Timeline:
23. June 2008 - Notified security_at_php.net
04. December 2008 - PHP developers released PHP 5.2.7
04. December 2008 - Public Disclosure
Recommendation:
It is recommended to upgrade to the latest version of PHP
which also fixes additional vulnerabilities reported by
third parties.
Grab your copy at:
http://www.php.net/get/php-5.2.7.tar.bz2/from/a/mirror
CVE Information:
The Common Vulnerabilities and Exposures project (cve.mitre.org) has
not assigned a name to this vulnerability yet.
GPG-Key:
pub 1024D/15ABDA78 2004-10-17 Stefan Esser <stefan.esser_at_sektioneins.de>
Key fingerprint = 7806 58C8 CFA8 CE4A 1C2C 57DD 4AE1 795E 15AB DA78
Copyright 2008 SektionEins GmbH. All rights reserved.
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