There's already a security update for iOS 13

iOS 13 was launched on Sept 19. — AFP Relaxnews

Apple has issued an important security update to its mobile operating system, after having just recently launched the latest version (iOS 13). The company has also released its first version of iPadOS, dedicated to tablets.

It is often recommended to be patient and never to install a major operating system update immediately after its launch. At Apple, this goes for both macOS and for iOS. Deployed on Sept 19, iOS 13 still has several bugs which are expected to be corrected by iOS 13.1 which became available Sept 24.