https://techcrunch.com/2019/08/26/apple-security-fix-jailbreak/

Apple has fixed a security flaw for a second time after it accidentally reintroduced an old bug in a recent software update.

iOS 12.4.1, released Monday, contains a security fix that was first patched months earlier in iOS 12.3. Apple rolled out a fix in May, but accidentally undid the security patch in its latest update, iOS 12.4, in July.