SteveWh - 8:42 am on May 23, 2012 (gmt 0)

That looks like an attempt to exploit the vulnerability in some PHP-as-CGI setups, which was discussed here and elsewhere a couple of weeks ago.

[php.net...]

It tries to use the PHP -d flag to set two php.ini entries.

The request got a 200 response because it was basically just a request for your home page, with the maliciously-intentioned query string added.