Mac Wi-Fi Update 1.0 can be downloaded from Apple's support site or through the Mac App Store on affected Macs.
About Mac Wi-Fi Update 1.0
This update is recommended for all late 2012 Mac systems. This update improves compatibility when using the 5GHz band in Wi-Fi.
Boot ROM or SMC Version Information: To confirm the update has been applied, the CFBundleVersion string of the AirPortBrcm4311.kext will need to be checked.
New driver delivered in update: AirPortBrcm4331.kext CFBundleVersion = 612.20.15