If you're using PHP 5.2.x, it's time to update.
The twelfth update to PHP 5.2 is now out with the PHP 5.2.12 release, providing fixes for five security flaws in addition to 61 other bugs that have now been patched.
Among the security fixes in PHP 5.2.12 is a new "max_file_uploads" directive. The new directive enables developers to set a maximum limit to file uploads, which could help to prevent a possible Denial of Service (DoS) attack vector.
There are also fixes for a pair of different bypass conditions, including a fix for a safe_mode bypass and an open_basedir bypass. The bypass conditions could potentially have enabled an attacker to get around php configurations to trigger some form of unwanted operation.
PHP 5.2.12 also provides additional input string validation for htmlspecialchars(), which is a function that converts special characters (such as ampersands) into HTML equivalents. The $_SESSION array that includes PHP session variables also gets a security boost with additional checks and protections for interrupt corruption.
PHP 5.3 itself was updated to version 5.3.1 at the end of November, fixing five security issues in addition to 133 bugs.
PHP is widely used as part of the LAMP (Linux/Apache/MySQL/PHP) Web application stack and remains a widely deployed language. A recent Elance report gave PHP its "MVP" award as the most consistently in-demand skill during 2009.