Programming PHP, 2nd Edition

Chapter 12. Security

PHP is a flexible language that has hooks into just about every API offered on the machines on which it runs. Because it was designed to be a forms-processing language for HTML pages, PHP makes it easy to use form data sent to a script. Convenience is a double-edged sword, however. The very features that let you quickly write programs in PHP can open doors for those who would break into your systems.

It’s important to understand that PHP itself is neither secure nor insecure. The security of your web applications is entirely determined by the code you write. For example, take a script that opens a file whose name was passed as a form parameter. If you don’t check the filename, the user can give a URL, an absolute pathname, or even a relative path to back out of the application data directory and into a personal or system directory.

Web application security is a young and evolving discipline. A single chapter on security cannot sufficiently prepare you for the onslaught of attacks your applications are sure to receive. This chapter takes a pragmatic approach and covers a distilled selection of topics related to security, including how to protect your applications from the most common and dangerous attacks. The chapter concludes with a list of additional resources that can help fill in the gaps as well as a brief recap that includes a few additional tips.