UpdateHostkeys now enabled by default

[Damien Miller]

On Sun, 4 Oct 2020, Christoph Anton Mitterer wrote:

> On Sat, 2020-10-03 at 19:44 +1000, Damien Miller wrote:
> > Otherwise, feel free to ask me anything.
> 
> Was it ever considered that the feature itself could be problematic,
> security-wise?

Of course we considered this.

> I see at least two candidates:
> - It's IMO generally a bad idea to distribute "better/newer" keys over
> a potentially already weaker trust path (i.e. something secured by the
> old key).

This is strictly no worse than continuing to use the old key, so I don't
consider it a problem.

> - If some key was compromised (and thus the server itself) an attacker
> might use the feature to distribute his own keys, which, during clean
> up from the attack, might be overseen.

How is this different to the status quo? If you don't clean up keys after
a compromise then you have a problem. Anyone doing this already has to
be prepared to deal with multiple keys being known for a host. The tooling
support for doing this (ssh-keygen -R) works identically regardless of
the number of keys.

-d