Kevin Waterson has posted a new article to his site today - an introductory look at security in your PHP applications.
One of the great benefits of PHP is its ease of access to new-comers. Its entry level is minimal and so attracts those looking for simple scripts to their sites. It is this same ease of access that becomes a problem as the new-comers begin to deal with input from users. Failure to adequately validate and sanitize data is the leading cause of security problems when dealing with PHP.
He looks at a few different areas that developers need to focus on (and be sure to filter on) like PHP_SELF, protection from email header injections, file inclusion and the use of error reporting to make handling user-generated errors "more correct".