While it is true it is a router that is no longer even sold at Apple, the Airport Extreme and Time Capsule bases receive timely security updates to address potential security or stability issues. The thing is, the AirPort Extreme and Time Capsule routers just got a new version with bug fixes.
In this case, the version 7.9.1 And as we say in them, they basically focus on closing a handful of security holes directly related to remote microcuts, memory leaks, errors when resetting the equipment or the unexpected deletion of user data previously entered in the routers.
A total of eight errors identified by Apple
In the notes of this new version, some details of the new version released are added and it makes an paragraph on connectivity problems in addition to those previously mentioned above. They close doors to possible third-party attacks and put in the hands of the user an important update for the operation of these routers, so we recommend updating as soon as possible to enjoy the fixes and avoid problems.
The new firmware updates released by Apple can be installed using the AirPort Utility application for iOS or MacOS and from now on it is possible to download and install the new versions on these devices. Apple stopped selling these devices a few months ago but that's no problem to release updates from time to time that solve detected failures or possible vulnerabilities of the equipment, in this Apple always responds.