A few weeks ago, Apple released a firmware update (version 7.9.1) for AirPorts Extreme and Time Capsule compatible with the 802.11ac standard; today the company has released one more update (verse 7.8.1), this time for the AirPorts Express, Extreme and Time Capsule compatible with the standard 802.11n.
According to Apple, the new update "improves the security of its base stations" is obviously recommended for all users.
It is worth noting that the company no longer sells its line of routers Ma officially stopped selling them in April 2018. Still, the company is required to support such products for up to five years after sales close then as well. It is possible that some updates will still appear here and there for such accessories.
To update, open AirPort Utility (either on macOS or iOS); Most likely the application will automatically report that there is an update available for your base; tap it and then tap "Update." 😉
Update by Rafael Fischmann 6/21/2019 4:12 PM
The Cybersecurity and Security Infrastructure Agency (Cybersecurity and Infrastructure Security Agency, or CISA) from the United States issued an alert recommending that all 802.11n compliant AirPorts Express, Extreme and Time Capsule owners apply update 7.8.1 released yesterday by Apple as soon as possible.
In fact, a new Apple support article details numerous security fixes brought about by the update.