This is a text-only version of the following page on https://raymii.org:

This is a text-only version of the following page on https://raymii.org:
---
Title : Restrict SSH
Author : Remy van Elst
Date : 20-01-2013
URL : https://raymii.org/s/software/Restrict_SSH.html
Format : Markdown/HTML
---

restrict _ssh.sh is a bash script which restricts ssh for a user to a set of
(flexible) commands via .ssh/authorized_ keys, and log it verbosely.

 Recently I removed all Google Ads from this site due to their invasive tracking, as well as Google Analytics. Please, if you found this content useful, consider a small donation using any of the options below: <a href="https://leafnode.nl">I'm developing an open source monitoring app called Leaf Node Monitoring, for windows, linux & android. Go check it out!</a> <a href="https://github.com/sponsors/RaymiiOrg/">Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.</a> <a href="https://www.digitalocean.com/?refcode=7435ae6b8212">You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $100 credit for 60 days. </a> 

### Purpose

I have a web application which needs to do some things over ssh on a server. It
runs as a separate user, and this script allows me to restrict the commands it
can execute as well. It however does allow regexes so filenames can be passed.
It also logs the commands and session info.

### Installation / Usage

Download the script from github, or clone the repository.

Put this script in the users home directory, or a directory which is accessible
by that user.

Edit the `allowed_commands` array:

declare -a allowed_commands=('^ls -[l|d|a]$' 'ls -la' 'w' 'uptime' 'pwd' 'uname -a')

Make sure that there are no comma's (`,`) between the options, otherwise it will
fail.

Make it executable for that user: `chown user:usergroup
/home/user/restrict_ssh.sh` and/or `chmod +x /home/user/restrict_ssh.sh`.

Modify the users `~/.ssh/authorized_keys` file, and before the ssh key(s) put
the line `command="/home/user/restrict_ssh.sh"` before the key. Like so:

command="/home/remy/restrict_ssh.sh" ssh-rsa AAAAB[...]X9t [email protected]

Optional: Disable password login for that user, edit `/etc/ssh/sshd_config` and
add the following:

Match User remy
PasswordAuthentication no

This will disable password logins only for user `remy`.

### Regexing / Safety

The default setup has a regex command allowed. It is the `ls` command, and the
regex allows either `ls -l`, `ls -d` or `ls -a`. If you know basic Perl style
regexes you can be very creative with this, for example `^ping -c 4
[a-zA-Z0-9]{2,20}.(com|org|net)$` allows the command ping to be executed for any
2 to 20 character .com, .net or .org domain. domain and nothing else.

_BE CAREFUL WITH THIS. IF YOU CONFIGURE IT WRONG USER MAY BE ABLE TO GET A SHELL
(vim, :!bash) OR OVERWRITE THE .ssh/authorized_ keys FILE. IF YOU ARE NOT SURE,
THEN DO NOT USE IT AT ALL!_

Also, if you allow `vim`, `less`, `man`, or any other program, a user might get
a shell. If the program you allow includes the possibility to run a shell, this
script/restriction is of no use.

### Logging

By default it logs lines like these to syslog:

Jan 20 20:39:23 vps11 RESTRICTED_SSH[9015]: INFO: SSH Connection: 'x.x.x.x 32309 x.x.x.x 22'
Jan 20 20:39:23 vps11 RESTRICTED_SSH[9014]: INFO: SSH Client: 'x.x.x.x 32309 22'
Jan 20 20:39:23 vps11 RESTRICTED_SSH[9017]: INFO: SSH Username: 'remy'
Jan 20 20:39:23 vps11 RESTRICTED_SSH[9016]: INFO: SSH Shell: '/bin/bash'
Jan 20 20:39:23 vps11 RESTRICTED_SSH[9013]: INFO: Sent SSH command: 'vim'
Jan 20 20:39:23 vps11 RESTRICTED_SSH[9018]: ERROR: Command "vim" is not allowed.

### Other info

I think it requires `Bash 4+` because of the array search function. I have no
bash lower than v4 to test it with.

### Links

<https://raymii.org/s/software/Restrict_SSH.html>
<https://github.com/RaymiiOrg/restrict_ssh>

[1]: https://www.digitalocean.com/?refcode=7435ae6b8212

---

License:
All the text on this website is free as in freedom unless stated otherwise.
This means you can use it in any way you want, you can copy it, change it
the way you like and republish it, as long as you release the (modified)
content under the same license to give others the same freedoms you've got
and place my name and a link to this site with the article as source.

This site uses Google Analytics for statistics and Google Adwords for
advertisements. You are tracked and Google knows everything about you.
Use an adblocker like ublock-origin if you don't want it.

All the code on this website is licensed under the GNU GPL v3 license
unless already licensed under a license which does not allows this form
of licensing or if another license is stated on that page / in that software:

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.

Just to be clear, the information on this website is for meant for educational
purposes and you use it at your own risk. I do not take responsibility if you
screw something up. Use common sense, do not 'rm -rf /' as root for example.
If you have any questions then do not hesitate to contact me.

See https://raymii.org/s/static/About.html for details.