openssh unix dev - Mar 2007 - login shell not found "bug"

Hello folks at OpenSSH,
  I recently encountered a behavior of your software (it doesn't really
deserve the name of "bug") that may be so rare that it is not worth
correcting--however, if it was corrected, it would have saved me many hours
of anguish. I recently set up a new PC with Ubuntu 6.10 and connected to my
office NIS domain. Unfortunately, when I tried to log in via SSH with my NIS
login, I always had my password rejected. I spent a great deal of time
trying to make sure that SSH had access to the NIS passwd file. It turned
out that the problem was that my default login shell in the NIS passwd file
was tcsh, and Ubuntu 6.10 does not come with tcsh installed by default. It
would have been wonderful if SSH could have told me that the reason my login
was failing was that my login shell didn't exist, rather than just rejecting
my password. I realize this doesn't happen very often, so it may not be
worth inserting, but I thought I would at least put it in your hands.

In any case, thank you for writing a program that 99% of the time I don't
notice because it works beautifully.

Regards,
Craig

Craig Bookwalter wrote:
> It turned out that the problem was that my default login shell in
> the NIS passwd file was tcsh, and Ubuntu 6.10 does not come with
> tcsh installed by default. It would have been wonderful if SSH could
> have told me that the reason my login was failing was that my login
> shell didn't exist, rather than just rejecting my password. I
> realize this doesn't happen very often, so it may not be worth
> inserting, but I thought I would at least put it in your hands.
First let me say that I am not one of the OpenSSH developers.  I am
speaking for myself.

Using a shell that is non-existent is a common way for admins to
disable accounts.  I don't know if sshd would have logged any
information to the syslog about it or not but returning an indication
to the user would probably be a security badness.  Because then an
attacker would learn something about the account, that the account
existed but that the shell did not.  That might give an attacker
information that could be used to advantage in breaking into the
system in another way.  The usual wisdom is give no system information
to an unauthorized user.  Therefore probably sshd cannot actually say
why the login is failing to the user logging into the system.

Did any errors get logged to the syslog with this information?  That
would be the right place for it.

This probably won't make you feel any better about it but perhaps it
does explain the situation a little more.  (And also that perhaps it
is time to think about switching to a more standard shell. :-)

Good Luck!
Bob