#478263 xdm: does not allow to log in when no password is set

Package:
xdm
Source:
xdm
Description:
X display manager
Submitter:
"Michal Suchanek"
Date:
2026-10-08 17:33:07 UTC
Severity:
normal
Tags:
#478263#5
Date:
2008-04-28 12:35:17 UTC
From:
To:
When I try to log in as a user with no password set xdm asks for a
password and fails to verify it. I have to set an empty password to make
xdm happy but this breaks other stuff.

Thanks

Michal
#478263#10
Date:
2008-10-21 05:38:35 UTC
From:
To:
found 478263 1:1.1.8-5
thank you

I can reproduce this problem.
#478263#17
Date:
2008-10-21 06:41:59 UTC
From:
To:
I can log in with no problem using login(8) on the tty, so I tried

    cp --backup /etc/pam.d/{login,xdm}
    /etc/init.d/xdm

This didn't help.  Nor does anything useful turn up in /var/log, even
with "debug" on all pam_unix.so entries in /etc/pam.d/common-*.

    Oct 21 17:08:49 Clio xdm[12858]: pam_unix(xdm:auth): authentication failure; logname= uid=0 euid=0 tty=:0 ruser= rhost=  user=twb
    Oct 21 17:08:51 Clio xdm[12858]: LOGIN FAILURE ON :0, (null)
    Tue Oct 21 17:08:51 2008 xdm error (pid 12858): pam_authenticate failure: Authentication failure
#478263#22
Date:
2008-10-21 11:34:56 UTC
From:
To:
This is because the moment xdm asks for a password it already failed
to log you in. It should verify that you actually do have a password
before asking for one.

Thanks

MS
#478263#27
Date:
2011-03-06 02:13:14 UTC
From:
To:
Hi,

Trent W. Buck <trentbuck@gmail.com> (21/10/2008):

if you'd like this bug to be looked at, you probably want to report it
upstream (product xorg, component App/xdm):
http://bugs.freedesktop.org/

KiBi.
#478263#32
Date:
2011-03-06 07:16:47 UTC
From:
To:
Cyril Brulebois <kibi@debian.org> (06/03/2011):

Actually, man xdm says:

       xlogin.Login.allowNullPasswd
              If set to ``true'', allow an otherwise failing password match to
              succeed  if the account does not require a password at all.  The
              default is ``false'', so only users that have passwords assigned
              can log in.

KiBi.
#478263#37
Date:
2011-03-07 11:45:48 UTC
From:
To:
Excerpts from Cyril Brulebois's message of Sun Mar 06 08:16:47 +0100 2011:
This is a discrepancy between login(1) and xdm then. login(1) allows
users with no password to log on without any issues or special settings.

Thanks

Michal
#478263#42
Date:
2011-03-07 22:57:52 UTC
From:
To:
Michal Suchanek wrote:

OTOH, openssh-server has an analogous setting.  Personally I have no
problem with this (assuming it works; I haven't tested it yet).
#478263#49
Date:
2026-10-08 17:30:35 UTC
From:
To:
tags 478263 + wontfix
thanks

On Mon, 28 Apr 2008 14:35:17 +0200 "Michal Suchanek" <michal.suchanek@ruk.cuni.cz> wrote:
 > Package: xdm
 > Severity: normal
 >
 >
 > When I try to log in as a user with no password set xdm asks for a
 > password and fails to verify it. I have to set an empty password to make
 > xdm happy but this breaks other stuff.

Hi,

This is intended and configurable behavior, so I am closing this bug.

As Cyril pointed out in 2011, xdm(8) documents the X resource
xlogin.Login.allowNumllPasswd. Unless this is set to true, xdm calls
pam_authenticate() with PAM_DISALLOW_NULL_AUTHTOK, which tells pam_unix
to reject empty passwords even though Debian's common-auth uses
"nullok". login(1) does not pass that flag, hence there is such difference. The
xdm default is the same policy choice as sshd's "PermitEmptyPasswords no".

To allow accounts without a password to log in via xdm, add

     xlogin.Login.allowNullPasswd: true

to /etc/X11/xdm/Xresources and restart xdm. Such accounts can then log in
with an empty password. This is still the case in xdm 1:1.1.17.

Thanks,
Boyuan Yang