This update is available for all Apple 802.11n Wi-Fi base stations including AirPort Express, AirPort Extreme, and AirPort Time Capsule.
It contains fixes that:
Note: This firmware update is for all 802.11n AirPort base stations.
For detailed information on AirPort base station and Time Capsule firmware updates, including instructions how to install the update, please visit:
All about Time Capsule, AirPort Extreme, and AirPort Express base station firmware updates
For more information on using AirPort Extreme or AirPort Express with your Internet account, contact your ISP or go to the AppleCare Knowledge Base at: http://www.apple.com/support/airport
For information on the security content of this update, please visit: http://support.apple.com/kb/HT1222
Addtional Information: How to set up and configure an 802.11g AirPort Extreme Base Station or AirPort Express in OS X Lion