"Theo de Raadt":

> > So if Firefox got compromised, it can still access my ssh-agent socket
> > that lives in /tmp.  Though, Firefox does not have access to ~/.ssh.
> 
> And what does firefox do then?

Enumerate the keys loaded into the agent, open an ssh connection
to cvs.openbsd.org, offer the agent key(s) for pubkey authentication,
forward the authentication request and response between the remote
server and ssh-agent, sucessfully log in as me, do whatever it
wants.

Probably won't work for me, because I have a U2F-backed ssh key,
so my YubiKey will start blinking for user confirmation, and I'll
be suspicious why it does so when I haven't started ssh or scp.

This scenario is also the reason why you shouldn't forward your
agent to a remote server that you don't trust.

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de