WordPress version 2.3.3 has been released. This release, like the previous one, addresses an urgent security vulnerability that was found in the WordPress XML-RPC implementation. The flaw could allow any valid user on your blog to edit posts made by other users on your blog.
WordPress 2.3.3 also fixes some other minor bugs. If you don’t care about those minor bug fixes and just want to patch your blog against the XML-RPC vulnerability, you can download a fixed copy of xmlrpc.php and copy it to your WordPress installation directory, replacing the existing xmlrpc.php file.
You’re probably better off just downloading WordPress 2.3.3 and doing the full upgrade.