Gentoo has issued a security advisory with a high impact rating affecting users of PHP <5.2.2.
Several vulnerabilities have been found in PHP, not least a huge number discovered by Stefan Esser during the infamous Month Of PHP Bugs (MOPB) including integer overflows in wbmp.c from the GD library and in the substr_compare() PHP 5 function.
There have also been reports of a buffer overflow in the make_http_soap_request() and in the user_filter_factory_create() functions as well as a buffer overflow in the bundled XMLRPC library. If that weren’t enough, the session_regenerate_id() and the array_user_key_compare() functions contain a double-free vulnerability. Oh, and let’s not forget the implementation errors in the Zend engine, in the mb_parse_str(), the unserialize() and the mail() functions and other elements.
The fact that remote attackers therefore have the potential ability to exploit these vulnerabilities in PHP applications which could, of course, lead to arbitrary code execution. And Denial of Service attacks. And scripted content execution within the context of an exploited site. And information leaks due to the bypassing of security.
And the workaround is? Err, it is non-existent actually. If you are a PHP 5 user then you really should make sure you are using the latest available version.