PHP Security Cheat Sheet
DRAFT CHEAT SHEET - WORK IN PROGRESS
This article is focused on providing PHP-specific guidance to securing web applications.
Don't use $_REQUEST - use $_GET or $_POST or $_SERVER instead
Use PDO with prepared statements or an ORM like Doctrine
Use a framework like Zend or Symfony - Stop re-writing the same code again and again
For Input validation use $_dirty['foo'] = $_GET['foo'] and then $foo = validate_foo($dirty['foo']);
5. Output encoding is entirely up to you. Just do it, ESAPI for PHP is ready for this job. 6. Not every PHP installation has a working mhash extension, so if you need to do hashing, check it before using it. Otherwise you can't do SHA-256 7. Not every PHP installation has a working mcrypt extension, and without it you can't do AES. Do check if you need it 8. Code with most of your code outside of the webroot. This is automatic for Symfony and Zend. Stick to these frameworks 9. Use PHP 5.3.8. Anything less is unsafe 10. There is no authentication or authorization classes in native PHP. Use ZF or Symfony instead 11. When developing PHP code, make sure you develop with PHP Unit and Jenkins - see http://qualityassuranceinphpprojects.com/pages/tools.html for more details. 12. Consider using Stefan Esser's Hardened PHP patch - http://www.hardened-php.net/suhosin/index.html (not maintained now, but the concepts are very poweful) 13. In terms of secure coding with PHP, do not use globals unless absolutely necessary - check your php.ini to ensure register_globals is off Do not run at all with this setting enabled It's extremely dangerous (register_globals has been disabled since 5.0 / 2006, but .... most PHP 4 code needs it, so many hosters have it turned on) THOUSANDS OF WEBSITES 14. Ensure allow_url_fopen and allow_url_include are both disabled to protect against RFI. But don't cause issues by using the pattern include $user_supplied_data or require "base" + $user_supplied_data - it's just unsafe as you can input /etc/passwd and PHP will try to include it 15. Eval() is evil() - It basically allows arbitrary PHP code execution, so do not evaluate user supplied input. and if you're not doing that, you can just use PHP directly. eval() is at least 10-100 times slower than native PHP 16. Watch for executable regexes (!) 17. Session rotation is very easy - just after authentication, plonk in session_regenerate_id() and you're done. 18. Set display_errors to 0, and set up logging to go to a file you control, or at least syslog. This is the most commonly neglected area of PHP configuration 19. Esoteric but important. Be aware of PHP filters - these are transparent to you and you need to know about them. php://input: takes input from the console gzip: takes compressed input and might bypass input validation http://au2.php.net/manual/en/filters.php