Basic Information

SSH or Secure Shell or Secure Socket Shell, is a network protocol that gives users a secure way to access a computer over an unsecured network.

Default port: 22

22/tcp open  ssh     syn-ack

Banner Grabbing

nc -vn <IP> 22

SSH could support weak cipher algorithms

This is discovered by default by nmap. But you can also use sslcan or sslyze.

Brute force usernames, passwords and private keys

Username Enumeration

In some versions of OpenSSH you can make a timing attack to enumerate users. You can use a metasploit module in order to exploit this:

msf> use scanner/ssh/ssh_enumusers

​Brute force​

Private/Public Keys BF

If you know some ssh private key that could be used... lets try it. You can use the nmap script:

https://nmap.org/nsedoc/scripts/ssh-publickey-acceptance.html

Or the MSF auxiliary module:

msf> use scanner/ssh/ssh_identify_pubkeys

Known badkeys can be found here:

You should look here in order to search for valid keys for the victim machine.

Default Credentials

Config files

ssh_config
sshd_config
authorized_keys
ssh_known_hosts
known_hosts
id_rsa

SFTP

You can configure SSH to behave as a SFTP server. So, some users will connect to SFTP service (in port 22) instead of to the SSH service.

You can even set a chroot to the SFTP users. A configuration example of SFTP users inside the file /etc/ssh/sshd_config can be seen in the following images.

All the ots-* users will be jailed inside a chroot.

SFTP Tunneling

If you have access to a SFTP server you can also tunnel your traffic through this for example using the common port forwarding:

sudo ssh -L <local_port>:<remote_host>:<remote_port> -N -f <username>@<ip_compromised> 

Symlink

The sftp have the command "symlink". Therefor, if you have writable rights in some folder, you can create symlinks of other folders/files. As you are probably trapped inside a chroot this won't be specially useful for you, but, if you can access the created symlink from a no-chroot service (for example, if you can access the symlink from the web), you could open the symlinked files through the web.

For example, to create a symlink from a new file "froot" to "/":

sftp> symlink / froot

If you can access the file "froot" via web, you will be able to list the root ("/") folder of the system.