Last week, a new iOS bug was discovered that could cause your iPhone to crash when it received a single character from the Indian language Telugu. Apple said that it would release an update to fix this issue before rolling out iOS 11.3 in the spring, and today that's precisely what it's done.
Apple today released iOS 11.2.6. According to Apple, the update "fixes an issue where using certain character sequences could cause apps to crash", which is almost certainly a reference to the Telugu bug.
This update also "fixes an issue where some third-party apps could fail to connect to external accessories".
This may be a small update, but that Telugu bug fix could be pretty annoying if someone sends the particular character to you, so you should probably grab iOS 11.2.6 as soon as you can. Head into Settings > General > Software Update do to it.
Apple today also released watchOS 4.2.3 and tvOS 11.2.6 updates.