Although Apple discontinued its line of AirPort base stations (routers), it recently released a firmware update, version 7.9.1. It fixes several security issues, one of which seems especially bad.
Impact: A base station factory reset may not delete all user information
Description: The issue was addressed with improved data deletion.
CVE-2019-8575: joshua stein
Check It Out: AirPort Base Stations Get 7.9.1 Firmware Update