MacRumors:
Apple today released iOS 17.3.1 and iPadOS 17.3.1, minor updates for the iOS 17 and iPadOS operating systems that were released in September 2023.
According to Apple's release notes, the update includes a fix for a bug that could cause text to unexpectedly duplicate or overlap while typing.
Source:

Apple Releases iOS 17.3.1 With Fix for Text Bug
Apple today released iOS 17.3.1 and iPadOS 17.3.1, minor updates for the iOS 17 and iPadOS operating systems that were released in September 2023....

Apple security releases - Apple Support
This document lists security updates and Rapid Security Responses for Apple software.