For those wondering whether their Macs are affected by the Thunderbolt vulnerability, I have checked the firmware update Apple has released and it seems these models specifically have been updated (and most likely affected):
iMac (21.5-inch, Late 2013) - iMac14,1/iMac14,3
iMac (27-inch, Late 2013) - iMac14,2
iMac (21.5-inch, Mid 2014) - iMac14,4
iMac (Retina 5K, 27-inch, Late 2014) - iMac15,1
MacBook Air (11-inch, Mid 2013)/(11-inch, Early 2014) - MacBookAir6,1
MacBook Pro (Retina, Mid 2012)/(Retina, 15-inch, Early 2013) - MacBookPro10,1
MacBook Pro (Retina, 13-inch, Late 2012)/(Retina, 13-inch, Early 2013) - MacBookPro10,2
MacBook Pro (Retina, 13-inch, Late 2013)/(Retina, 13-inch, Mid 2014) - MacBookPro11,1
MacBook Pro (Retina, 15-inch, Late 2013)/(Retina, 15-inch, Mid 2014) - MacBookPro11,2
Mac mini (Late 2014) - Macmini7,1
Mac Pro (Late 2013) - MacPro6,1
Unfortunately, it seems like it's only available for Yosemite users. Though I'm fairly certain it should affect Mavericks users and possibly earlier OS's.