20018—Remote Code Execution - CVE-2012-1823

Some PHP versions, when configured to run using CGI, do not correctly handle query strings that lack an unescaped “=” character, enabling arbitrary code execution. In this case, an operating system command was caused to be executed on the web server, and the results were returned to the web browser.

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.