As indicated in the information that accompanies the update, the firmware update is certified for draft 2.0 of 802.11ne includes a series of security updates and bug fixes.
Apple indicates that the software addresses a security problem that could allow a remote attacker to disrupt network performance. The problem is related to the way the IPv6 protocol handles the type of the routing headers. The update solves this problem by deactivating support for said type of headers.
This issue does not affect newer 802.11n base stations equipped with Gigabit Ethernet ports, according to Apple.