Allow SFTP but disallow SSH?

Question

I'm starting a very little hosting company for a few friends and little clients, nothing big.

I want to give my "clients" the right to manage their files on the server. I hate FTP as it is not secure and it's in my opinion obsolete.

So I'd like to allow my users to connect through SFTP but not allow them to connect through SSH. (I know, I know, SFTP is using SSH). But I was just wondering, is it possible?

So I wouldn't have to install a FTP service on the server and everything would be awesome!

Answer 1

Starting with version 4.9 OpenSSH (not available in centos 5.x but ChrootDirectory feature was backported) has an internal-sftp subsystem:

Subsystem sftp internal-sftp

And then block other uses:

Match group sftponly
     ChrootDirectory /upload
     X11Forwarding no
     AllowTcpForwarding no
     AllowAgentForwarding no
     ForceCommand internal-sftp -d /%u

Add your users to the sftponly group. The chroot directory must be owned by root, and cannot be group-writeable, so create a subdirectory for each user that's owned by the appropriate user (if you match their home directory, it will be the default working directory when connecting). I'd also set /bin/false as the user's shell.

As an example, users can then upload single files with:

sftp username@hostname <<< 'put filename.ext /'

(scp will hopefully soon be modified to use sftp so this will become easier)

Answer 2

There is a shell scponly what does this. It can chroot too.

Answer 3

Checkout rssh which is a fake shell that allows sftp but denies ssh

More about RSSH

http://www.pizzashack.org/rssh/

RPMs

http://pkgs.repoforge.org/rssh/

You can configure rssh to allow / deny different behaviours like sft, scp etc.

Answer 4

The solution from Rob Wouters need only a minor change... as I could not comment for lack of points, I'll just reproduce here how it worked for me.

The directory you chroot to in sshd_config, really need to belong to root and not writable by any other user or group. So, if you put

ChrootDirectory /upload/%u

the user directory specified by '%u' must comply to the same rule. If you don't, you'll get "bad ownership or modes for chroot directory" error. Instead, you put only the base directory and pass the user owned and writable directory to the ForceComand. See below:

# override default of no subsystems
#Subsystem      sftp    /usr/lib/openssh/sftp-server
Subsystem       sftp    internal-sftp

Match group sftponly
     ChrootDirectory /upload
     X11Forwarding no
     AllowTcpForwarding no
     AllowAgentForwarding no
     ForceCommand internal-sftp -d /%u

Now, when the user logs in, the internal-sftp will change de current directory to the right place.

Answer 5

I use the method of specifying the user shell as /bin/false as mentioned. However, you must ensure that /bin/shell is in /etc/shells. Then it works ssh=no ftp=ok.

I also use vsftpd and add this
chroot_local_user=YES to /etc/vsftpd/vsftpd.conf so that ftp-ers can't see date other then their own.

Advantage to these simple changes are no annoying config to ssh config for each user.

Answer 6

Configuring ssh to enable only sftp for some selected users is a good idea and it works properly, provided that you you install either scponly or rssh.

rssh works fine, unless you need to configure jail, in this case try to follow instruction provided by CHROOT manuals is crazy, leading to "copy" large parts of system executables and library just below "each user jail", including rssh shell itself. It is a space-wasting method.

scponly needs a deep understanding in configuration leading to ever-present problem of login rejection in case of jail setup.

The straightforward way to allow "ftp" functionalities with jail properly working, SSL/TLS support for secure transactions and login is to use an "old-but-working" VSFTPD, which installs quickly and cleanly and offers all configurability as needed and, last but not least: it works!

Maurizio.

Answer 7

You can modify /etc/passwd and give that user a fake shell so that he can not use ssh.

Answer 8

Don't forget to find the line UsePAM yes and comment it:

#UsePAM yes

Without disabling this, your SSH server would crash on reloading/restarting. Since you do not need fancy functions of PAM, this is fine.

Answer 9

This is the way i set up SFTP and disallowing SSH.

please do the following:

1. First create sftp user and group sftp

2. Create separate directory as root for the SFTP files: sudo mkdir -p /home/sftpdir

3. Have a tested sshd_config file that allows SSH over port 22 but also SFTP on random port for security reasons

#$OpenBSD: sshd_config,v 1.101 2017/03/14 07:19:07 djm Exp $
# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.
# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin
# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options override the
# default value.

Port 38250 Port 22 PasswordAuthentication no 
ChallengeResponseAuthentication no

# 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 X11Forwarding yes PrintMotd no
# Allow client to pass locale environment variables AcceptEnv LANG LC_*
#DenyUsers sftpuser

# override default of no subsystems Subsystem       sftp    internal-sftp 
Match group sftp 
Match User sftpuser 
Match LocalPort 38250 
ForceCommand internal-sftp 
ChrootDirectory /home/sftpdir 
PermitTunnel no 
AllowAgentForwarding no 
X11Forwarding no    
AllowTcpForwarding no

4. Restart and check status of sshd service

    sudo service sshd restart
    
    service sshd status

5. Create a Shell file. Add execution to echo a notification message

    sudo touch /bin/sftponly
    echo -e '#!/bin/sh\necho "This account is limited to SFTP access only."' | sudo tee -a  /bin/sftponly

6. Give execution permissions and append to shells file

    sudo chmod a+x /bin/sftponly
    echo "/bin/sftponly" | sudo tee -a /etc/shells

7. finally Test and you should not be able to connect.

8. A template to use SFTP client with a SSH key and basic verbosity:

    sftp -v -oPort=$RANDOM_PORT -i ~/.ssh/$SSH_KEY.pem sftpuser@$HOST