20017—Source Code Disclosure - CVE-2012-1823

Some PHP versions, when configured to run using CGI, do not correctly handle query strings that lack an unescaped “=” character, enabling PHP source code disclosure, and arbitrary code execution. In this case, the contents of the PHP file were served directly to the web browser. This output will typically contain PHP, although it may also contain straight HTML.

Upgrade to the latest stable version of PHP, or use the Apache web server and the mod_rewrite module to filter out malicious requests using the "RewriteCond" and "RewriteRule" directives.