This blog post is to increase awareness of the release of firmware 3.9.3. When we first posted this firmware the other day, it was available in the blog or in controllers 5.6.x only.
This morning we pushed firmware 3.9.3 to controllers 5.5.20 and later, as well as posted it to our download site (see HERE). The controller will only check for new firmware once every 24 hours. You can manually initiate a firmware check by going to Settings>Maintenance>Check Firmware Update. A few moments later you should see an upgrade button available on the Devices page.
Firmware 3.9.3 containts the station (STA) mode fixes for any UniFi Access Points that would be vulnerable to KRACK. For more details on that, please see the disclosure website found HERE. We also have a help centre article available HERE, which covers UniFi devices as well as other Ubiquiti devices.