If you're running MediaWiki on a 32-bit platform, you should upgrade
to PHP 5.3.5, PHP 5.2.17 or a patched version of PHP from a Linux
distribution which includes a fix for CVE-2010-4645. If you run
MediaWiki on a 32-bit platform with an earlier version of PHP, you
will be vulnerable to a denial-of-service vulnerability.
CVE-2010-4645 is a vulnerability which causes the conversion from a
string to a floating-point number to take forever, for certain special
strings. PHP's weak typing means that such conversion can take place
implicitly, for example in code like "$string > 0". I can confirm that
MediaWiki has modules which will convert user input to a
floating-point number. Conversion can be triggered by an attacker with
no special privileges.
PHP release announcement:
http://www.php.net/archive/2011.php#id2011-01-06-1
Updated Ubuntu packages:
http://www.ubuntu.com/usn/usn-1042-1
-- Tim Starling