This is a serious bug as an attacker could capture or modify data via network by bypassing SSL/TLS verification. Apple released updates for patching this bug in both iOS 6 and iOS 7, which are 6.1.6 and 7.0.6 respectively. Currently, there is no update for OS X but be sure that there will be one pretty soon.
You can use this website https://gotofail.com which tests if your browser is vulnerable or not.
You can update your iPhone, iPad or iPod fast by doing an OTA (Over the air) update by going to Settings>General>Software Update>Update (It is highly recommended though to mainly update through iTunes).