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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@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@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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