ssh-vulnkey doesnt check all keys. Also, it would be nice to extend the warning message.

[LimCore]

Not all keys can be checked with ssh-vulnkey, and users forget that they need to take care of servers used by them that did accept the weak keys.
I think we should at least warn about that.

Details:

1) ssh-vulnkey can not check DSA keys that are in non standard locations, or that are on removable media like usb keys.
At least inform user about that and instruct to run ssh-vulnkey by hand.
More sure solution: modify ssh to always check the key that is about to be used.
But more work (and double check! i.e. do not store the key being check in /tmp or something!)

2) someone should probably warn users that just installing the fix, and regenerating the key
is not enough to be 100% safe from this bug consequences, that is:

a) servers that where set to accept the weak key may have been already compromised. To be really sure,
admin should reinstall them.
b) the same for your own box, if you log into own box using public key
c) remember to remove wrong keys from .authorized_keys or update server software to do that (or warn server admin)

I'm not security specialist, so I first consulted the above with advanced users, admins, developers.
I also noted how most "regular users" thought that just installing upgrade is enought and they can forget about the issue.

I dont want to read on slashdot next month how thousands small serves where compromised because users didnt realize that
they told servers to accept their weak keys and server where not maintained well, so please - lets warn the users.

[LimCore (limcore)]

There are already scripts to exploits servers that where used via pubkey by ubuntu/debian users ( http://packetstormsecurity.org/0805-exploits/debian-sploit.txt )

I really think now would be a time to at least extend the warning message to inform briefly about this problem.

[Kees Cook (kees)]

Hi, thanks for the report. Note that openssh-vulnkey can be aimed at specific files to check them. As for education, I think Ubuntu has already taken drastic measures to inform users of the need to replace the old keys (SSH won't even accept them any more).