iOS Rapid Security Response: what is Apple update 16.4 a, how to download it, what does it do - do I need it?

For the first time ever, Apple has made a Rapid Security Response (RSR) update available to iPhone users, along with a corresponding for Mac, marking a change in how the company rolls out smaller updates.

Apple has not yet made clear what security updates are included in the RSR, or why it was released in the first place, but its release suggests the identification of a potential critical security vulnerability.

However, the company might prefer to wait until the majority of users have had a chance to install the update before revealing specifics about the vulnerabilities it fixes. Here is everything you need to know about them.

What are Rapid Security Responses?

Rapid Security Responses (RSRs) are a new type of software release for iPhone, iPad and Mac. They deliver security updates in between software updates, such as upgrades to the WebKit framework stack, the Safari web browser or other vital system libraries.

Instead of waiting for a scheduled update to the iOS operating system - which are released on a regular basis, typically several times a year - Apple can quickly rectify reported security issues with a Rapid Security Response, mitigating risks from potential software exploits before the damage becomes too widespread.

How do I download them?

Your device will automatically apply Rapid Security Responses by default, and will prompt you to restart it if necessary. But if for any reason the RSR is not applied automatically, open the Settings app on the device and then choose General, then Software Update. Next, choose Download and Install.

To ensure that your device will automatically download and apply future RSRs, Apple says you should “go to Settings > General > Software Update > Automatic Updates, then make sure ’Security Responses & System Files’ is turned on.”

If you choose to disable this setting or decide not to use Rapid Security Responses when they become available, your device will get the necessary fixes or mitigations when they are added through a subsequent software update.

Only the most recent versions of iOS, iPadOS, and macOS will receive new Rapid Security Responses, starting with iOS 16.4.1, iPadOS 16.4.1 and macOS 13.3.1. All iPhones released from late 2017 onwards, including the iPhone 8, iPhone 8 Plus and iPhone X, are compatible with Apple iOS 16.4.

Once the update is installed, your device should display that it is using iOS 16.4.1 (a). Users on Mac devices will be running macOS 13.3.1 (a).

Do I need to download them?

Apple hasn’t specified what the security updates in iOS 16.4.1 (a) include, or exactly why the RSR was rolled out in the first place. But the release of a Rapid Security Responses implies the discovery of a potentially serious security flaw.

Apple may prefer to hold off on disclosing details about the vulnerabilities that RSR update fixes until the majority of users have had a chance to download it. It could be that the company reveals the specifics of the update at a later date, but we will just have to wait and see.

Users who have been able to upgrade do not yet seem to have encountered any major issues. That makes sense, as RSR updates are intended to be smaller and less disruptive than previous iOS security patches.