Bug#611218: openssh-server: "PermitRootLogin no" doesn't prevent Root from logging in over ssh

[Phil Armstrong <phil@kantaka.co.uk>]

Package: openssh-server
Version: 1:5.5p1-6
Severity: normal
Tags: squeeze

My /etc/ssh/sshd_config says:

PermitRootLogin no

yet I can still log in from another machine to root:

  phil@xanthus ~
  $ ssh -S none arod.local -l root
  root@arod.local's password: 
  Linux arod 2.6.32-5-powerpc #1 Fri Dec 10 16:30:49 UTC 2010 ppc

  The programs included with the Debian GNU/Linux system are free software;
  the exact distribution terms for each program are described in the
  individual files in /usr/share/doc/*/copyright.
 
  Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
  permitted by applicable law.
  Last login: Wed Jan 26 20:45:14 2011 from 217.155.153.12
  root@arod:~# 

This is a stock Debian squeeze powerpc install, with no tweaks.


-- System Information:
Debian Release: 6.0
  APT prefers testing
  APT policy: (650, 'testing')
Architecture: powerpc (ppc)

Kernel: Linux 2.6.32-5-powerpc
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_GB.UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages openssh-server depends on:
ii  adduser                 3.112+nmu2       add and remove users and groups
ii  debconf [debconf-2.0]   1.5.36           Debian configuration management sy
ii  dpkg                    1.15.8.8         Debian package management system
ii  libc6                   2.11.2-9         Embedded GNU C Library: Shared lib
ii  libcomerr2              1.41.12-2        common error description library
ii  libgssapi-krb5-2        1.8.3+dfsg-4     MIT Kerberos runtime libraries - k
ii  libkrb5-3               1.8.3+dfsg-4     MIT Kerberos runtime libraries
ii  libpam-modules          1.1.1-6.1        Pluggable Authentication Modules f
ii  libpam-runtime          1.1.1-6.1        Runtime support for the PAM librar
ii  libpam0g                1.1.1-6.1        Pluggable Authentication Modules l
ii  libselinux1             2.0.96-1         SELinux runtime shared libraries
ii  libssl0.9.8             0.9.8o-4         SSL shared libraries
ii  libwrap0                7.6.q-19         Wietse Venema's TCP wrappers libra
ii  lsb-base                3.2-23.2squeeze1 Linux Standard Base 3.2 init scrip
ii  openssh-blacklist       0.4.1            list of default blacklisted OpenSS
ii  openssh-client          1:5.5p1-6        secure shell (SSH) client, for sec
ii  procps                  1:3.2.8-9        /proc file system utilities
ii  zlib1g                  1:1.2.3.4.dfsg-3 compression library - runtime

Versions of packages openssh-server recommends:
ii  openssh-blacklist-extra       0.4.1      list of non-default blacklisted Op
ii  xauth                         1:1.0.4-1  X authentication utility

Versions of packages openssh-server suggests:
pn  molly-guard                   <none>     (no description available)
pn  rssh                          <none>     (no description available)
pn  ssh-askpass                   <none>     (no description available)
pn  ufw                           <none>     (no description available)

-- debconf information:
* ssh/use_old_init_script: true
  ssh/vulnerable_host_keys:
  ssh/encrypted_host_key_but_no_keygen:
  ssh/disable_cr_auth: false

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin no
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile	%h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes