http://wordpress.org/development/200...urity-release/
Yesterday a vulnerability was discovered: a specially crafted URL could be requested that would allow an attacker to bypass a security check to verify a user requested a password reset. As a result, the first account without a key in the database (usually the admin account) would have its password reset and a new password would be emailed to the account owner. This doesn’t allow remote access, but it is very annoying.
I'm not sure if it is worth upgrading specifically for this, but, if you're not in the 2.8.x series, it would be worth upgrading.