How to upgrade brew ssh after recent client exploit?
To be able to modify certain directories/files in OS X El Capitan you have to disable System Integrity Protection (SIP) AKA “rootless”:


Reboot your Mac into Recovery Mode by restarting your computer and holding down cmd+R until the Apple logo appears on your screen.
In the menubar click Utilities > Terminal.
In the Terminal window, type in csrutil disable.
Restart your Mac.
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.