Some useful tricks using OpenSSH

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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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10. . SSH replaces FTP.
sftp host.domena.pl
sftp> dir
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Assem Chelli
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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 ??
.
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 ??
.
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 ??
.
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 ??
.
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 ??
.
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
.
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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
OpenSSH tricks
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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
.
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
OpenSSH tricks
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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
.
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
.
Assem Chelli
OpenSSH tricks
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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
.
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
.
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
.
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 !
.
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 !
.
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 !
.
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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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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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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52. . Tunneling types
LocalForward
RemoteForward
DynamicForward
ProxyCommand
ForwardX11/ForwardX11Trusted Tunnel
ControlMaster
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53. . Security
ssh-agent
X11
GatewayPorts
MITM
SSH-1.99
SSH timing attack
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54. Appendix
. Questions
Questions?
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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
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