For those wondering what this security flaw is, it seems that this is a vulnerability in WebKit where it would let hackers create a website that could then execute code that users are unaware of. According to Apple, “Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.”
As Apple’s comment seems to suggest, it seems that there might have already been some attacks that take advantage of this vulnerability already out there in the wild, meaning that this isn’t something that was brought to Apple’s attention that hadn’t been exploited yet, so it’s probably a good idea for you to update your devices ASAP if you don’t want to fall prey to such attacks.
The update should already be live so if you don’t want to wait to be prompted on your iPhone or iPad, simply head on over to the iPhone or iPad’s Settings app, tap on General, then go to Software Update and it should list iOS 15.3.1 or iPadOS 15.3.1 as being available for download.