Although it seems that Apple has really abandoned its line of Wi-Fi routers (even though they are highly praised out there), the latest models continue to receive proper support from the company.
Today, practically a year after the last update, Apple released new firmware versions for AirPorts Express, Extreme and Time Capsule.
IEEE 802.11ac bases are now receiving the version 7.7.9 AirPort Base Station Firmware Update, while older, 802.11n, receive the version 7.6.9.
As pointed out in the Apple support articles linked above, the updates have to do with that KRACK vulnerability released in mid-October – which had already been fixed on all Apple operating systems, itself, but not on these routers. They also correct other security holes detected by the Apple team, so they are highly recommended to all users.
Updates can now be applied by AirPort Utility macOS (located in the / Applications / Utilities / folder) or by its own iOS app: