[Secure-testing-team] Bug#586480: openssh-server: chroot directive is not working when using FISH (File transfer of shell with midnight commander)

[Andre Rodier]

Package: openssh-server
Version: 1:5.1p1-5
Severity: critical
Tags: security
Justification: root security hole

Hello,

I have successfully configured my ssh server to chroot users, by followinf the directives described here:
http://www.debian-administration.org/articles/590 ie. OpenSSH SFTP chroot() with ChrootDirectory

The chroot option seems to work well when I use the sftp command, ie I cannot see any directory at all.

However, if I use the fish protocol [1] included in midnight commander, I can see the full filesystem hierarchy,
and even transfer files from the etc folder, etc...

I don't know if it's a configuration problem on my side, but if there is an option do disallow fish
when using chroot, that need to be explicitly specified. Otherwise, debian users may relay
on a chrooted server that can be bypassed by a simple manipulation...


[1] http://en.wikipedia.org/wiki/Files_transferred_over_shell_protocol

Kind regards,
André Rodier.

Here my ssh config: See the end for chroot config

-----8<------------------------------------------------------------
# Package generated configuration file
# See the sshd(8) 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 DEBUG

# 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_*

UsePAM no
UseDNS no

#ChrootDirectory 
# Subsystem sftp /usr/lib/openssh/sftp-server
Subsystem sftp internal-sftp
Match group sftponly
        ChrootDirectory /home/%u
        X11Forwarding no
        AllowTcpForwarding no
	AllowAgentForwarding no
        ForceCommand internal-sftp
-----8<------------------------------------------------------------

-- System Information:
Debian Release: 5.0.3
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.26-2-amd64 (SMP w/1 CPU core)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages openssh-server depends on:
ii  adduser         3.110                    add and remove users and groups
ii  debconf [debcon 1.5.24                   Debian configuration management sy
ii  dpkg            1.14.29                  Debian package management system
ii  libc6           2.7-18lenny4             GNU C Library: Shared libraries
ii  libcomerr2      1.41.3-1                 common error description library
ii  libkrb53        1.6.dfsg.4~beta1-5lenny4 MIT Kerberos runtime libraries
ii  libpam-modules  1.0.1-5+lenny1           Pluggable Authentication Modules f
ii  libpam-runtime  1.0.1-5+lenny1           Runtime support for the PAM librar
ii  libpam0g        1.0.1-5+lenny1           Pluggable Authentication Modules l
ii  libselinux1     2.0.65-5                 SELinux shared libraries
ii  libssl0.9.8     0.9.8g-15+lenny6         SSL shared libraries
ii  libwrap0        7.6.q-16                 Wietse Venema's TCP wrappers libra
ii  lsb-base        3.2-20                   Linux Standard Base 3.2 init scrip
ii  openssh-blackli 0.4.1                    list of default blacklisted OpenSS
ii  openssh-client  1:5.1p1-5                secure shell client, an rlogin/rsh
ii  procps          1:3.2.7-11               /proc file system utilities
ii  zlib1g          1:1.2.3.3.dfsg-12        compression library - runtime

Versions of packages openssh-server recommends:
pn  openssh-blacklist-extra       <none>     (no description available)
pn  xauth                         <none>     (no description available)

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)

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