The page in question notes that an application may be able to execute arbitrary code with kernel privileges. An the update is meant to fix that, which is a long way of saying the update is meant to prevent jailbreaking. And the CVE code provided at the bottom makes a clear reference to unc0ver.
The Unc0ver jailbreak, as noted by Wired, is notable as it’s able to jailbreak up-to-date Apple devices. Specifically, it can jailbreak devices running iOS 11 all the way up to iOS 13.5. And while using it, the jailbreak still allowed the use of the company’s services like iCloud and iMessage. But with the iOS 13.5.1 update, it looks like that has come to an end. Not entirely surprising, as Apple would be one of the faster companies to react to what it sees as a gap in its security. (Source: Apple via The Verge, Wired)
