FYI: SSH1 now disabled at compile-time by default

[Damien Miller]

On Tue, 24 Mar 2015, Dan Kaminsky wrote:

> Alright, so I pulled the data from scans.io,  There's actually 82,650
> devices on the open Internet claiming support for <=SSH-1.5, generally
> routers.  Top 20 on that is:
[snip]

> Of course, this is out of a total of 15,124,618 SSH servers, granting a
> compat rate greater than 99.99%.

OK, so most of the <0.01% of users are network administrators - a
fairly technical audience and one that I doubt would have trouble
procuring a v.1 capable ssh client. I bet the majority of admins
wouldn't even be using OpenSSH as the client.

> However, distinctly and painfully unlike
> SSL/TLS, SSH is successfully deployed and used on internal networks that
> cannot be scanned from the open Internet.  It's also a protocol of fairly
> critical importance, uniquely used in a "hop by hop" manner in which each
> hop actually has to work.

Not really, people can port-forward. Besides, the most common hop-by-hop
configuration is the gateway bastion, which also happens to be the 1)
the most important to keep up to date and 2) the easiest to fix (since
you only need to fix the bastion).

> 7.3% of Cisco routers on the open Internet only support SSHv1.  The numbers
> inside private networks are likely to be higher.
> 
> I can see the argument for pushing people to upgrade, but not by surprise in
> a minor version.  If SSH is going to block old insecure versions it has a
> much bigger problem, because upgrade rates on SSH on the Internet are
> actually not fantastic.  Here's the top 40 across all versions of SSH:
> 
> $ head -n 40 sshall_versions.txt
> 2412684 SSH-2.0-OpenSSH_5.3
>  984056 SSH-2.0-OpenSSH_4.3
>  936855 SSH-2.0-dropbear_0.51
>  854624 SSH-2.0-dropbear_0.46
>  798414 SSH-2.0-OpenSSH_6.0p1
[snip]

This brings to light another point: we can turn off v.1 by default at
our end, but it won't filter through to what the majority of users see
for several years.

> This is specifically a scenario where OpenSSH should measure twice and cut
> once.  The worst case scenario is that people update even less than they
> already do, because who knows what servers are no longer important enough to
> require connectivity to next.

> Start the discussion, absolutely

We started the discussion _14 years ago_ by making protocol 2 the default.

We prodded people _8 years ago_ by making protocol 2 the only thing
supported on the server for new installs.

We prodded people again _6 years ago_ by requiring explicit configuration
at both client and server to enable v.1 at all.

At this point, I don't think any further discussion is going to make any
difference. Do you think another two years would make an appreciable
change to the numbers you posted above, beyond old hardware literally
dying of old age?

-d