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The understanding of the systems architecture is essential to analize its security. PHP file upload architecture:

1. Files are transferred from client filesystem to server RAM.
2. Apache process will check httpd.conf and php.ini directives.
3. Once completed, file will be dumped into the server’s default temporary directory, unless another location has been given with the upload_tmp_dir directive in php.ini. The temporary directory used for storing files must be writable by apache user.
4. After a correct transfer, if track_vars is enabled (always since 4.0.3), $_FILES superglobal array is defined (is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods). Only name and type are provided by the user, and therefore tmp_name, error, and size are provided by PHP. The related variables will be initialized as globals if register_globals is enabled (must be desactivated).
5. The control is given to the php script to move the file to another location. If not, the temp file will be automatically unlinked at the end of the script.

• Directives in a php.ini file
  • upload_max_filesize = 10M
  • post_max_size = 20M
• .htaccess file
  • php_value upload_max_filesize 10M
  • php_value post_max_size 20M
  
  
  The PHP documentation states that the memory_limit setting also affects file uploading. Generally speaking, memory_limit should be larger than post_max_size.
  
  

  • memory_limit = 16M to your php.ini file (recommended, if you have access)

  With root access, you can use the sed util in Linux/Unix based systems, in order to increace the memory for 64M. Don’t forget to properly locate you php.ini file!

  sed -i 's/memory_limit = 16M/memory_limit = 64M/' /etc/php5/apache2/php.ini
  • ini_set('memory_limit', '16M'); to your sites/default/settings.php file
  • php_value memory_limit 16M to your .htaccess file in root