PHP Security Advisory: Vulnerability in PHP versions 4.2.0 and 4.2.1 

Issued on: July 22, 2002 
Software: PHP versions 4.2.0 and 4.2.1 
Platforms: All 

   The PHP Group has learned of a serious security vulnerability in PHP 
   versions 4.2.0 and 4.2.1. An intruder may be able to execute arbitrary 
   code with the privileges of the web server. This vulnerability may be 
   exploited to compromise the web server and, under certain conditions, 
   to gain privileged access. 

Description 

   PHP contains code for intelligently parsing the headers of HTTP POST 
   requests. The code is used to differentiate between variables and files 
   sent by the user agent in a "multipart/form-data" request. This parser 
   has insufficient input checking, leading to the vulnerability. 

   The vulnerability is exploitable by anyone who can send HTTP POST 
   requests to an affected web server. Both local and remote users, even 
   from behind firewalls, may be able to gain privileged access. 

Impact 

   Both local and remote users may exploit this vulnerability to compromise 
   the web server and, under certain conditions, to gain privileged access. 
   So far only the IA32 platform has been verified to be safe from the 
   execution of arbitrary code. The vulnerability can still be used on IA32 
   to crash PHP and, in most cases, the web server. 

Solution 

   The PHP Group has released a new PHP version, 4.2.2, which incorporates 
   a fix for the vulnerability. All users of affected PHP versions are 
   encouraged to upgrade to this latest version. The downloads web site at 

      http://www.php.net/downloads.php 
    
   has the new 4.2.2 source tarballs, Windows binaries and source patches 
   from 4.2.0 and 4.2.1 available for download. 
  
  
Workaround 

   If the PHP applications on an affected web server do not rely on HTTP 
   POST input from user agents, it is often possible to deny POST requests 
   on the web server. 

   In the Apache web server, for example, this is possible with the 
   following code included in the main configuration file or a top-level 
   .htaccess file: 

      <Limit POST> 
          Order deny,allow 
          Deny from all 
      </Limit> 
     
   Note that an existing configuration and/or .htaccess file may have 
   parameters contradicting the example given above. 

  
Credits 

   The PHP Group would like to thank Stefan Esser of e-matters GmbH for 
   discovering this vulnerability. 
    

Copyright (c) 2002 The PHP Group.