Apple has kept its promise and released an update that fixes a character error that could cause device waves iPhone, Apple Watch, Apple TV and Mac computers.
IOS 11 will remain in Apple's history as one of the most problematic releases released. Read:
So operating systems for iOS, macOS, watchOS and tvOS can be updated immediately.
Updates are: iOS 11.2.6 (15D100), MacOS High Sierra 10.13.3 Supplemental Update (17D102 / 17D2102), tvOS 11.2.6 (15K600), and watchOS 4.2.3 (15S600b) and are available for download.
According to Apple's release notes, new software updates fix a problem where some character sequences could cause some applications to collapse.
In more technical terms, updates fix a memory corruption problem that Apple encountered by improving the input validation to CoreText.
In any case, it would be good to update your devices immediately.