FYI, Apple yesterday released a patch for OS X El Capitan 10.11.6, macOS Sierra 10.12.6, and macOS High Sierra 10.13: https://support.apple.com/en-us/HT208221
“Wi-Fi
Available for: macOS High Sierra 10.13, macOS Sierra 10.12.6, OS X El Capitan 10.11.6
Impact: An attacker in Wi-Fi range may force nonce reuse in WPA clients (Key Reinstallation Attacks - KRACK)
Description: A logic issue existed in the handling of state transitions. This was addressed with improved state management.
CVE-2017-13077: Mathy Vanhoef of the imec-DistriNet group at KU Leuven
CVE-2017-13078: Mathy Vanhoef of the imec-DistriNet group at KU Leuven
CVE-2017-13080: Mathy Vanhoef of the imec-DistriNet group at KU Leuven”