Apple has already patched the KRACK attack WPA2 Wi-Fi vulnerability in the developer and public betas for iOS, watchOS, tvOS, and macOS.
Update: Apple sent me the following statement on the KRACK exploit, confirming the upcoming patches:
"Apple is deeply committed to protecting our customers' data. The fix for the KRACK WiFi vulnerability is currently in the betas of iOS, macOS, watchOS and tvOS and will soon be rolled out to customers."
KRACK is an exploit that attacks the way WPA2 protects Wi-Fi access points. While it's bad, there are a are a few factors that prevent it from being truly damaging to the state of modern wireless networking.
First, it can be patched. We don't need a new standard like we did when WEP was broken and everyone had to move to WPA2.
From the KRAK Q&A:
implementations can be patched in a backwards-compatible manner. This means a patched client can still communicate with an unpatched access point (AP), and vice versa. In other words, a patched client or access point sends exactly the same handshake messages as before, and at exactly the same moment in time.
Second, in some cases, access points won't need to be updated.
Our main attack is against the 4-way handshake, and does not exploit access points, but instead targets clients. So it might be that your router does not require security updates. We strongly advise you to contact your vendor for more details. In general though, you can try to mitigate attacks against routers and access points by disabling client functionality (which is for example used in repeater modes) and disabling 802.11r (fast roaming).
For example, it's my understanding that Apple's AirPorts, including Express, Extreme, and Time Capsule don't seem be vulnerable to the exploit, even if using one as a bridge.
If you're using a different router, we're maintaining a list of updates that you can consult as needed. If in doubt, contact your vendor directly.
For ordinary home users, your priority should be updating clients such as laptops and smartphones.
Third, Apple has confirmed to me that the KRACK exploit has already been patched in iOS, tvOS, watchOS, and macOS betas.
As soon as the updates leave beta, they'll be pushed out to everyone. We'll have to wait and see how fast other manufacturers are to respond, and how many of our connected devices receive updates.
Updated to reflect the need for both client and point-of-access updates, if and when available.