Apple is rolling out iOS 11.2.1 update for eligible iPhone, iPad, and iPod touch devices, as well as tvOS 11.2.1 update for the Apple TV, both of which restore HomeKit sharing after a remote access bug was spotted last week. iOS 11.2.1 is now available to download for iPhone 5s and later, iPad Air and later, and iPod touch 6th generation. tvOS 11.2.1 is available for Apple TV 4 and 4k variants.
The reason for a simultaneous software update is because it restores HomeKit for shared users, a feature that was recently disabled due to a bug that was spotted last week. This bug was responsible for giving unauthorised access in vulnerable circumstances. With the new updates, for both platforms, Apple has promptly restored access for all users. In its release notes, Apple says, "iOS 11.2.1 fixes bugs including an issue that could disable remote access to shared users of the Home app."
The security bulletin that accompanied the updates reveals that HomeKit bug allowed a remote attacker to unexpectedly alter application state, and that the message handling issue was addressed with improved input validation.
iPhone, iPad, and iPod touch users can download this update by going into Settings > General > Software Update and checking for the update. Once it appears, click on Download and Install; the update will automatically get installed on the device. It is advisable to use a Wi-Fi connection to download the over-the-air update. Also, you should back up your data, and ensure that your device has over 50 percent of charge or connected to a power source before beginning the update process.
On your Apple TV, the update can be installed in a similar manner by going into Settings > System > Software Updates in tvOS. Once downloaded, the update will restart the Apple TV once. Do note that tvOS 11.2.1 is available on the Apple TV 4K over the air only. On the Apple TV 4, although, you can install the update manually by downloading the IPSW file through iTunes.
Just last week, iOS 11.2 was rolled out to all eligible Apple iPhone, iPad, and iPod users. This major update brought new features like support for Apple Pay Cash and faster wireless charging support. tvOS 11.1 was also updated last month but brought minimal upgrades to the Apple TV.