Apple released iOS 13.5.1 on June 1, and as is traditional, Apple has now stopped signing iOS 13.5, making downgrading to that version of iOS no longer possible. iOS 13.5.1 fixes a security hole that enabled the unc0ver 5.0 jailbreak.
Apple released a similar fix for tvOS, watchOS, and macOS, patching the vulnerability across all of its devices.
Apple is known to stop signing older versions of operating systems after it releases a public update, as part of an effort to encourage users to keep their devices’ operating systems up to date.
The iOS 13.5.1 update fixed the following security flaw:
Kernel
Available for: iPhone 6s and later, iPad Air 2 and later, iPad mini 4 and later, and iPod touch 7th generation
Impact: An application may be able to execute arbitrary code with kernel privileges
Description: A memory consumption issue was addressed with improved memory handling.
CVE-2020-9859: unc0ver