This document discusses OpenSSH and provides tricks for using SSH. It begins by explaining what SSH is and why it is important for secure remote access. It then discusses installing OpenSSH and basic SSH usage like remote login. The document covers additional SSH features like executing commands remotely, file transfers using SCP and SFTP, public key authentication, and default configuration files. It provides examples of SSH port forwarding, comparing remote and local files, and mounting remote folders. The document concludes with a list of "best SSH tricks" including enabling password-less login and starting tunnels.

1. .
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OpenSSH tricks
Assem Chelli
assem.ch@gmail.com (@assem_ch)
Hacknowledge Contest Algeria 2013
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Assem Chelli
OpenSSH tricks
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2. . What is SSH?
SSH: Secure SHell, a Network protocol Created by Tatu
Ylonen (1995)
Secure logging into remote computer
Public key authentication (!Password),
Authentication of the server (!MAN-IN-THE-MIDDLE )
Encryption,
Integrity
more features:
Stream Compression
Port forwarding
X11 sessions forwarding
File transfer
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Assem Chelli
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3. . WHY SSH IS SO IMPORTANT?
IP spoofing
IP source routing
DNS spoofing
Password sniffing
Manipulation of transfer data Atack on X11 (sniffing on
authorization)
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Assem Chelli
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4. . Install Open SSH
SSH is so resricted , OPEN SSH is free!
openssh-client , openssh-server
sudo apt-get install openssh-client openssh-server
sudo yum install openssh-client openssh-server
WINDOWS: download & install PuTTY
http://www.chiark.greenend.org.uk/ sgtatham/putty/
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Assem Chelli
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5. . Basic SSH usage
Remote login
ssh hostname
ssh -l user hostname
ssh user@hostname
cd:41:70:30:48:07:16:81:e5:30:34:66:f1:56:ef:db
RSA key fingerprint —> yes / no (Public Key
authentification)
host’s password: _______ (Password authentification)
known hosts
~/.ssh/known_hosts
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Assem Chelli
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6. . Basic SSH usage
Remote login
ssh hostname
ssh -l user hostname
ssh user@hostname
cd:41:70:30:48:07:16:81:e5:30:34:66:f1:56:ef:db
RSA key fingerprint —> yes / no (Public Key
authentification)
host’s password: _______ (Password authentification)
known hosts
~/.ssh/known_hosts
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Assem Chelli
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7. . Omar in the middle!
let’s play SERVER role!
We put Server offline
Someone fix his IP as the same IP of server
Now try login again
ssh host
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle
attack)!
It is also possible that the RSA host key has just been changed.
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Assem Chelli
OpenSSH tricks
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8. . Omar in the middle!
let’s play SERVER role!
We put Server offline
Someone fix his IP as the same IP of server
Now try login again
ssh host
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle
attack)!
It is also possible that the RSA host key has just been changed.
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Assem Chelli
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9. . SSH replaces telnet.
ssh host.domena.pl
ssh user@host.domena.pl
ssh -l user host.domena.pl
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Assem Chelli
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10. . SSH replaces FTP.
sftp host.domena.pl
sftp> dir
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Assem Chelli
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11. . SSH replaces r-command .
rexec
ssh host "cat /etc/passwd"
rlogin
ssh user@host
rcp
scp file host.domena.pl
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Assem Chelli
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12. . Executing commands remotely
ssh host netstat
ssh host "ls -C /bin"
ssh host “cat /etc/passwd”
ssh host “vi /tmp/foo ”
ssh -t host vi /tmp/foo
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Assem Chelli
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13. . Executing commands remotely
ssh host netstat
ssh host "ls -C /bin"
ssh host “cat /etc/passwd”
ssh host “vi /tmp/foo ”
ssh -t host vi /tmp/foo
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Assem Chelli
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14. . Redirecting commands input and output
ssh host "ls /bin | grep -i rm"
ssh host "ls /bin" | grep -i rm
ssh host "cat /etc/passwd" > remote_passwd
ssh host "psql billing" < billing.sql | grep -v ^INFO
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Assem Chelli
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15. . Redirecting commands input and output
ssh host "ls /bin | grep -i rm"
ssh host "ls /bin" | grep -i rm
ssh host "cat /etc/passwd" > remote_passwd
ssh host "psql billing" < billing.sql | grep -v ^INFO
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Assem Chelli
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16. . File transfer
scp
scp [user1@]host1:/path/to/source/file
[user2@]host2:/path/to/destination/file
scp -r
sftp
sftp host
sftp> cd /usr/share/games
sftp> ls
sftp> lcd /tmp
get c*
quit
tar-over-ssh
ssh host "cd /usr/share/games ; tar cf - ./a*" |
> (cd /tmp ; tar xpvf -)
rsync
rsync -ve ssh host:/bin/c* /tmp
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Assem Chelli
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17. . Public Keys
Generate a public key
ssh-keygen -t rsa
cat ~/.ssh/id_rsa.pub
Authentification
ssh-add -l
Restrictions
cat ~/.ssh/authorized_keys
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Assem Chelli
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18. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
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19. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
OpenSSH tricks
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20. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
OpenSSH tricks
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21. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
OpenSSH tricks
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22. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
OpenSSH tricks
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23. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
OpenSSH tricks
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24. . Default Config Files and SSH Port
/etc/ssh/sshd_config - OpenSSH server configuration file.
/etc/ssh/ssh_config - OpenSSH client configuration file.
~/.ssh/ - Users ssh configuration directory.
~/.ssh/authorized_keys - Lists the public keys (RSA or
DSA) that can be used to log into the users account
/etc/nologin - If this file exists, sshd refuses to let anyone
except root log in.
/etc/hosts.allow and /etc/hosts.deny : Access controls
lists that should be enforced by tcp-wrappers are defined here.
SSH default port : TCP ??
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Assem Chelli
OpenSSH tricks
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25. . BEST SSH Tricks 1
. Copy ssh keys to user@host to enable password-less ssh logins
1
ssh-copy-id user@host
. Start a tunnel from some machines port 80 to your local post
2001
2
ssh -N -L2001:localhost:80 somemachine
. Output your microphone to a remote computers speaker
3
dd if=/dev/dsp | ssh -c arcfour -C username@host dd
of=/dev/dsp
. Compare a remote file with a local file
4
ssh user@host cat /path/to/remotefile | diff /path/to/localfile
-
. Mount folder/filesystem through SSH
5
ss hfs name@server:/path/to/folder /path/to/mount/point
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Assem Chelli
OpenSSH tricks
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26. . BEST SSH Tricks 1
. Copy ssh keys to user@host to enable password-less ssh logins
1
ssh-copy-id user@host
. Start a tunnel from some machines port 80 to your local post
2001
2
ssh -N -L2001:localhost:80 somemachine
. Output your microphone to a remote computers speaker
3
dd if=/dev/dsp | ssh -c arcfour -C username@host dd
of=/dev/dsp
. Compare a remote file with a local file
4
ssh user@host cat /path/to/remotefile | diff /path/to/localfile
-
. Mount folder/filesystem through SSH
5
ss hfs name@server:/path/to/folder /path/to/mount/point
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Assem Chelli
OpenSSH tricks
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27. . BEST SSH Tricks 1
. Copy ssh keys to user@host to enable password-less ssh logins
1
ssh-copy-id user@host
. Start a tunnel from some machines port 80 to your local post
2001
2
ssh -N -L2001:localhost:80 somemachine
. Output your microphone to a remote computers speaker
3
dd if=/dev/dsp | ssh -c arcfour -C username@host dd
of=/dev/dsp
. Compare a remote file with a local file
4
ssh user@host cat /path/to/remotefile | diff /path/to/localfile
-
. Mount folder/filesystem through SSH
5
ss hfs name@server:/path/to/folder /path/to/mount/point
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Assem Chelli
OpenSSH tricks
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28. . BEST SSH Tricks 1
. Copy ssh keys to user@host to enable password-less ssh logins
1
ssh-copy-id user@host
. Start a tunnel from some machines port 80 to your local post
2001
2
ssh -N -L2001:localhost:80 somemachine
. Output your microphone to a remote computers speaker
3
dd if=/dev/dsp | ssh -c arcfour -C username@host dd
of=/dev/dsp
. Compare a remote file with a local file
4
ssh user@host cat /path/to/remotefile | diff /path/to/localfile
-
. Mount folder/filesystem through SSH
5
ss hfs name@server:/path/to/folder /path/to/mount/point
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Assem Chelli
OpenSSH tricks
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29. . BEST SSH Tricks 1
. Copy ssh keys to user@host to enable password-less ssh logins
1
ssh-copy-id user@host
. Start a tunnel from some machines port 80 to your local post
2001
2
ssh -N -L2001:localhost:80 somemachine
. Output your microphone to a remote computers speaker
3
dd if=/dev/dsp | ssh -c arcfour -C username@host dd
of=/dev/dsp
. Compare a remote file with a local file
4
ssh user@host cat /path/to/remotefile | diff /path/to/localfile
-
. Mount folder/filesystem through SSH
5
ss hfs name@server:/path/to/folder /path/to/mount/point
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Assem Chelli
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30. . BEST SSH Tricks 2
. SSH connection through host in the middle
1
ssh -t reachable_host ssh unreachable_host
. Copy from host1 to host2, through your host
2
ssh root@host1 cd /somedir/tocopy/ && tar -cf . | ssh
root@host2 cd /samedir/tocopyto/ && tar -xf -
. Run any GUI program remotely
3
ssh -fX @
. Create a persistent connection to a machine
4
ssh -MNf @
. Attach screen over ssh
5
ssh -t remote_host screen -r
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Assem Chelli
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31. . BEST SSH Tricks 2
. SSH connection through host in the middle
1
ssh -t reachable_host ssh unreachable_host
. Copy from host1 to host2, through your host
2
ssh root@host1 cd /somedir/tocopy/ && tar -cf . | ssh
root@host2 cd /samedir/tocopyto/ && tar -xf -
. Run any GUI program remotely
3
ssh -fX @
. Create a persistent connection to a machine
4
ssh -MNf @
. Attach screen over ssh
5
ssh -t remote_host screen -r
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Assem Chelli
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32. . BEST SSH Tricks 2
. SSH connection through host in the middle
1
ssh -t reachable_host ssh unreachable_host
. Copy from host1 to host2, through your host
2
ssh root@host1 cd /somedir/tocopy/ && tar -cf . | ssh
root@host2 cd /samedir/tocopyto/ && tar -xf -
. Run any GUI program remotely
3
ssh -fX @
. Create a persistent connection to a machine
4
ssh -MNf @
. Attach screen over ssh
5
ssh -t remote_host screen -r
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Assem Chelli
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33. . BEST SSH Tricks 2
. SSH connection through host in the middle
1
ssh -t reachable_host ssh unreachable_host
. Copy from host1 to host2, through your host
2
ssh root@host1 cd /somedir/tocopy/ && tar -cf . | ssh
root@host2 cd /samedir/tocopyto/ && tar -xf -
. Run any GUI program remotely
3
ssh -fX @
. Create a persistent connection to a machine
4
ssh -MNf @
. Attach screen over ssh
5
ssh -t remote_host screen -r
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Assem Chelli
OpenSSH tricks
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34. . BEST SSH Tricks 2
. SSH connection through host in the middle
1
ssh -t reachable_host ssh unreachable_host
. Copy from host1 to host2, through your host
2
ssh root@host1 cd /somedir/tocopy/ && tar -cf . | ssh
root@host2 cd /samedir/tocopyto/ && tar -xf -
. Run any GUI program remotely
3
ssh -fX @
. Create a persistent connection to a machine
4
ssh -MNf @
. Attach screen over ssh
5
ssh -t remote_host screen -r
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Assem Chelli
OpenSSH tricks
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35. . BEST SSH Tricks 3
. Run complex remote shell cmds over ssh
1
ssh host -l user $(
ssh host -l user cat cmd.txt
. Resume scp of a big file
2
rsync partial progress rsh=ssh $file_source
$user@$host:$destination_file
. Analyze traffic remotely over ssh w/ wireshark
3
ssh root@server.com tshark -f port !22 -w - | wireshark -k -i -
. Have an ssh session open forever
4
autossh -M50000 -t server.example.com screen -raAd
mysession
. Harder, Faster, Stronger SSH clients
5
ssh -4 -C -c blowfish-cbc
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Assem Chelli
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36. . BEST SSH Tricks 3
. Run complex remote shell cmds over ssh
1
ssh host -l user $(
ssh host -l user cat cmd.txt
. Resume scp of a big file
2
rsync partial progress rsh=ssh $file_source
$user@$host:$destination_file
. Analyze traffic remotely over ssh w/ wireshark
3
ssh root@server.com tshark -f port !22 -w - | wireshark -k -i -
. Have an ssh session open forever
4
autossh -M50000 -t server.example.com screen -raAd
mysession
. Harder, Faster, Stronger SSH clients
5
ssh -4 -C -c blowfish-cbc
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Assem Chelli
OpenSSH tricks
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37. . BEST SSH Tricks 3
. Run complex remote shell cmds over ssh
1
ssh host -l user $(
ssh host -l user cat cmd.txt
. Resume scp of a big file
2
rsync partial progress rsh=ssh $file_source
$user@$host:$destination_file
. Analyze traffic remotely over ssh w/ wireshark
3
ssh root@server.com tshark -f port !22 -w - | wireshark -k -i -
. Have an ssh session open forever
4
autossh -M50000 -t server.example.com screen -raAd
mysession
. Harder, Faster, Stronger SSH clients
5
ssh -4 -C -c blowfish-cbc
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Assem Chelli
OpenSSH tricks
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38. . BEST SSH Tricks 3
. Run complex remote shell cmds over ssh
1
ssh host -l user $(
ssh host -l user cat cmd.txt
. Resume scp of a big file
2
rsync partial progress rsh=ssh $file_source
$user@$host:$destination_file
. Analyze traffic remotely over ssh w/ wireshark
3
ssh root@server.com tshark -f port !22 -w - | wireshark -k -i -
. Have an ssh session open forever
4
autossh -M50000 -t server.example.com screen -raAd
mysession
. Harder, Faster, Stronger SSH clients
5
ssh -4 -C -c blowfish-cbc
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Assem Chelli
OpenSSH tricks
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39. . BEST SSH Tricks 3
. Run complex remote shell cmds over ssh
1
ssh host -l user $(
ssh host -l user cat cmd.txt
. Resume scp of a big file
2
rsync partial progress rsh=ssh $file_source
$user@$host:$destination_file
. Analyze traffic remotely over ssh w/ wireshark
3
ssh root@server.com tshark -f port !22 -w - | wireshark -k -i -
. Have an ssh session open forever
4
autossh -M50000 -t server.example.com screen -raAd
mysession
. Harder, Faster, Stronger SSH clients
5
ssh -4 -C -c blowfish-cbc
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Assem Chelli
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40. . Best SSH tricks 4
. Disable OpenSSH Server
1
apt-get remove openssh-server (ubuntu )
chkconfig sshd off && yum erase openssh-server (fedora)
. Force to use SSH protocole 2 because SSH-1 is vulnerable
(Man-in-the-middle attacks)
2
in /etc/ssh/sshd_config add the line: Protocol 2
. Limit root or Users’ SSH Access
3
in /etc/ssh/sshd_config
find&modify the line: AllowUsers root assem
or find&modify the line: DenyUsers omar zaki ali-baba
or find&modify the line: PermitRootLogin no
or create /etc/nologin
. Enable a Warning Banner
4
in /etc/ssh/sshd_config add the line: Banner /etc/issue
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Assem Chelli
OpenSSH tricks
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41. . Best SSH tricks 4
. Disable OpenSSH Server
1
apt-get remove openssh-server (ubuntu )
chkconfig sshd off && yum erase openssh-server (fedora)
. Force to use SSH protocole 2 because SSH-1 is vulnerable
(Man-in-the-middle attacks)
2
in /etc/ssh/sshd_config add the line: Protocol 2
. Limit root or Users’ SSH Access
3
in /etc/ssh/sshd_config
find&modify the line: AllowUsers root assem
or find&modify the line: DenyUsers omar zaki ali-baba
or find&modify the line: PermitRootLogin no
or create /etc/nologin
. Enable a Warning Banner
4
in /etc/ssh/sshd_config add the line: Banner /etc/issue
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Assem Chelli
OpenSSH tricks
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42. . Best SSH tricks 4
. Disable OpenSSH Server
1
apt-get remove openssh-server (ubuntu )
chkconfig sshd off && yum erase openssh-server (fedora)
. Force to use SSH protocole 2 because SSH-1 is vulnerable
(Man-in-the-middle attacks)
2
in /etc/ssh/sshd_config add the line: Protocol 2
. Limit root or Users’ SSH Access
3
in /etc/ssh/sshd_config
find&modify the line: AllowUsers root assem
or find&modify the line: DenyUsers omar zaki ali-baba
or find&modify the line: PermitRootLogin no
or create /etc/nologin
. Enable a Warning Banner
4
in /etc/ssh/sshd_config add the line: Banner /etc/issue
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Assem Chelli
OpenSSH tricks
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43. . Best SSH tricks 4
. Disable OpenSSH Server
1
apt-get remove openssh-server (ubuntu )
chkconfig sshd off && yum erase openssh-server (fedora)
. Force to use SSH protocole 2 because SSH-1 is vulnerable
(Man-in-the-middle attacks)
2
in /etc/ssh/sshd_config add the line: Protocol 2
. Limit root or Users’ SSH Access
3
in /etc/ssh/sshd_config
find&modify the line: AllowUsers root assem
or find&modify the line: DenyUsers omar zaki ali-baba
or find&modify the line: PermitRootLogin no
or create /etc/nologin
. Enable a Warning Banner
4
in /etc/ssh/sshd_config add the line: Banner /etc/issue
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Assem Chelli
OpenSSH tricks
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44. . Best SSH tricks 5
. Change SSH port
1
in /etc/ssh/sshd_config find&modify the line: Port 300
. Deny empty passwords
2
in /etc/ssh/sshd_config find&modify the line:
PermitEmptyPasswords no
. Use SSH as an Internet Proxy
3
Google it !
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Assem Chelli
OpenSSH tricks
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45. . Best SSH tricks 5
. Change SSH port
1
in /etc/ssh/sshd_config find&modify the line: Port 300
. Deny empty passwords
2
in /etc/ssh/sshd_config find&modify the line:
PermitEmptyPasswords no
. Use SSH as an Internet Proxy
3
Google it !
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Assem Chelli
OpenSSH tricks
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46. . Best SSH tricks 5
. Change SSH port
1
in /etc/ssh/sshd_config find&modify the line: Port 300
. Deny empty passwords
2
in /etc/ssh/sshd_config find&modify the line:
PermitEmptyPasswords no
. Use SSH as an Internet Proxy
3
Google it !
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Assem Chelli
OpenSSH tricks
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47. . Best SSH tricks 5
. Change SSH port
1
in /etc/ssh/sshd_config find&modify the line: Port 300
. Deny empty passwords
2
in /etc/ssh/sshd_config find&modify the line:
PermitEmptyPasswords no
. Use SSH as an Internet Proxy
3
Google it !
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Assem Chelli
OpenSSH tricks
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48. . Thwart SSH Crackers
DenyHosts
Fail2ban
security/sshguard
security/sshblock
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Assem Chelli
OpenSSH tricks
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49. . SSH via Proxy!
Proxy Problem!
/etc/ssh/ssh_config
host *
proxyCommand connect -H 10.0.0.1:80 %h %p
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Assem Chelli
OpenSSH tricks
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50. . SSH via Proxy!
Proxy Problem!
/etc/ssh/ssh_config
host *
proxyCommand connect -H 10.0.0.1:80 %h %p
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Assem Chelli
OpenSSH tricks
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51. . forwarding over SSH
Agent forwarding
ssh -A trustedhost (your privatekeys can be stolen)
X11 forwarding
ssh -X user@host firefox
ssh -Y user@host
Port forwarding
ssh -L8000:anotherhost:80 somehost
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Assem Chelli
OpenSSH tricks
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52. . Tunneling types
LocalForward
RemoteForward
DynamicForward
ProxyCommand
ForwardX11/ForwardX11Trusted Tunnel
ControlMaster
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Assem Chelli
OpenSSH tricks
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53. . Security
ssh-agent
X11
GatewayPorts
MITM
SSH-1.99
SSH timing attack
.
Assem Chelli
OpenSSH tricks
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54. Appendix
. Questions
Questions?
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Assem Chelli
OpenSSH tricks
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55. Appendix
For Further Reading
. For Further Reading I
SSH tips, tricks & protocol tutorial
.Damien Miller , AUUG Winter 2002 .
25 Best SSH Commands / Tricks.
http://www.newitperson.com/2012/01/25-ssh-commandstricks/
SSH manpage
.
Assem Chelli
OpenSSH tricks
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