From csirt.cy
Apple released iOS 12.4.1 today to fix a security flaw reintroduced with the release of iOS 12.4, and used by security researcher Pwn20wnd to develop and release a jailbreak tool for up-to-date iOS devices.
The vulnerability patched today by Apple is a use after free tracked as CVE-2019-8605 targeted by the Sock Puppet exploit that was used to create jailbreak tools for iOS devices.
The flaw was discovered by Google Project Zero’s Ned Williamson, was previously patched by Apple with the iOS 12.3 release from May 13, and was now re-patched in iOS 12.4.1.