In brief: Coming in at around 80 MB (depending on your iPhone), Apple's minor iOS 13.5.1 update blocks one of the more powerful jailbreaking tools to have come out recently. The company has also released updates for watchOS, iPadOS, HomePod, and Apple TV.
Unc0ver's jailbreaking tool came out less than two weeks ago, with the main highlight being its capability to run on Apple's then-current iOS 13.5. Cupertino, however, has leapfrogged it in its latest iOS 13.5.1 update, released specifically to block this tool.
Under the Settings app, Apple briefly notes that "iOS 13.5.1 provides important security updates and is recommended for all users," while its support page details that the patch addresses the Unc0ver vulnerability and is meant to prevent apps from executing arbitrary code with kernel privileges.
Although jailbreaking still remains a somewhat niche activity, tools that enable it are usually indicative of vulnerabilities in Apple's operating systems, known to those outside the company. Unc0ver is said to be capable of jailbreaking all iOS versions (11 and onwards) and Apple's swift response to blocking this tool in the latest software update arrives when a vast majority (93%) of iPhones are currently running iOS 13 or iOS 12.
This patch, however, seems unlikely to address problems that some users have been facing following the iOS 13.5 update. Most complaints have pointed to increased battery drain, iPads stuck in reboot loops, and broken media playback for MP4/MPEG-4 files.
Affected users might have expected today's update to fix these issues but it seems they'll have to wait a few more days or weeks until Apple rolls out another patch.