How to upgrade brew ssh after recent client exploit?

Solution 1:

To be able to modify certain directories/files in OS X El Capitan you have to disable System Integrity Protection (SIP) AKA “rootless”:

  1. Reboot your Mac into Recovery Mode by restarting your computer and holding down cmd+R until the Apple logo appears on your screen.
  2. In the menubar click Utilities > Terminal.
  3. In the Terminal window, type in csrutil disable.
  4. Restart your Mac.
  5. After finishing your mods re-enable it in Recovery Mode with csrutil enable.

The file /System/Library/LaunchAgents/org.openbsd.ssh-agent.plist may be replaced in the next system update.