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Advisory 05/2006: Zend Platform Multiple Remote Vulnerabilities
From: Stefan Esser <sesser () hardened-php net>
Date: Thu, 24 Aug 2006 13:29:54 +0200

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                        Hardened-PHP Project
                        www.hardened-php.net

                      -= Security  Advisory =-


     Advisory: Zend Platform Multiple Remote Vulnerabilities
 Release Date: 2006/08/24
Last Modified: 2006/08/24
       Author: Stefan Esser [sesser () hardened-php net]

  Application: Zend Platform <= 2.2.1
     Severity: Malformed session ids may lead to multiple security problems
         Risk: Critical
Vendor Status: Vendor has a released an updated version
   References: http://www.hardened-php.net/advisory_052006.128.html


Overview:

   Quote from http://www.zend.com/downloads
   "Zend Platform is the all-in-one production environment that ensures 
   your PHP applications are available, fast, reliable and scalable. It 
   uniquely guarantees application uptime and reliability through 
   enhanced PHP monitoring and immediate problem resolution."
   
   During the development of suhosin, which is our new PHP protection
   module, several compatibility tests with binary 3rd party PHP 
   extensions like the Zend Platform and the Zend Optimizer have been 
   made. When testing the session protection features of suhosin, we 
   discovered that the session clustering system, which is shipping
   with the Zend Platform is vulnerable to several different attacks.
   
   By exploiting these vulnerabilities, an attacker can crash the 
   session clustering daemon, which leads to a malfunction of the
   session function and renders the attacked node useless. By
   carefully crafting the attack session IDs, an attacker might
   be able to either execute code within the context of the 
   session clustering daemon or within the mod_cluster module,
   which is the communication link between PHP and the daemon.
   
   Additionally a directory traversal vulnerability in the disk 
   storage module allows creating and reading the session file 
   anywhere on the hard disk. If for example a directory or file 
   within the document root of the webserver is writeable by the 
   session clustering daemon (which by default runs with the same 
   privileges as the webserver), this can lead to arbitrary PHP 
   code injection. On the other hand it might be possible to upload
   a user defined file to the webserver and craft a session identifier
   so that the data inside the file is used as session data.
   This obviously leads to total control over the content of the
   session and therefore to control over the application.


Details:

   The Zend Platform comes with a session handler module that plugs
   itself into the session management of PHP to support session
   clustering. This module communicates with the ZendSessionManager 
   daemon. This daemon is responsible for transffering session data
   between nodes and does most of the work.
   
   Our analysis revealed that both components, the clustering
   module mod_cluster and the daemon, itself have problems with
   malicious session identifiers. By default the session identifier
   is retrieved from the PHPSESSID request variable. Our first
   observation was that sending the identifier as a string with
   length 0 immediately crashed the mod_cluster module. The next
   observation was that an overlong session identifier also leads
   to a crash.
   
   Analysing the responsible code within a debugger revealed that
   a statement like:    
   
         strncpy(dst, src, strlen(src+1))
          
   was used to copy the session identifier around. This is obvisouly
   broken and leads to an overflow in the BSS segment, which makes
   exploitation tricky, because the data behind the buffer is not
   directly used again. However a later debugging session has shown
   that when some conditions are triggered mod_cluster crashed
   because the instruction pointer address was changed.
   
   The other observation was that the long PHPSESSID never reached
   the daemon. This changed when we took into account the special
   layout of Zend Platform session identifiers. They look something
   like this:
   
         xxxxxxxx:yyyyyyyy:00000000:0000...00:l8uqsu49p....
   
   This special format encodes extra data into the first part of
   the session identifier that determines the IP of the node 
   creating it. With this information it is possible for the daemon
   to contact the node that is responsible for storing the session.
   
   When the session data is stored on the hard disk, the last 
   component of the session identifier is used directly to create
   the filename. Unfortunately this is again performed without any
   size check. Therefore the filename might overflow its buffer. In
   our tests overflowing with a long string resulted in a crash
   inside glibc free(). Depending on the system's implementation of
   malloc(), this can lead to code execution.
   
   The final observation was that the last component of the session
   identifier also allows directory traversal attacks on the place
   where the session file is stored. This obviously allows creating
   the session files anywhere on the hard disk, where the daemon has
   write privileges. And to use any file on the hard disk as origin
   for the session data. The later is very dangerous if the 
   application allows uploading files and the user is able to
   predict its storage location. By uploading a file that contains
   session data in a daemon compatible format, it is possible to get
   total control over the session data, the application uses.
   
   The ability to write session files for example into writeable 
   directories within the document root path can lead to PHP code 
   execution if the attacker is either able to put PHP code into a 
   programm variable that is stored within the session (some session 
   management systems store for example the User-Agent in the session 
   to make session hijacking/fixation a little bit harder). 
   
   Additionally in PHP < 4.4.3 and < 5.1.4, session identifiers are 
   not limited in their charset for 3rd party session handlers. 
   Therefore on these systems it is possible to have PHP code directly 
   in the session identifier. Because the last component of the 
   session identifier is also directly copied into the session file 
   this ensures that PHP code is within the file.


Proof of Concept:

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


Disclosure Timeline:

   21. August 2006 - Contacted Zend by email
   24. August 2006 - Zend released an updated Zend Platform
   24. August 2006 - Public Disclosure


Recommendation:

   It is strongly recommended to upgrade to the newest version of
   Zend Platform (2.2.1a) which you can download at:

   http://www.zend.com/download


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 2006 Stefan Esser. All rights reserved.

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