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22 - Pentesting SSH/SFTP

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
SSH servers:
  • ​openSSH – OpenBSD SSH, shipped in BSD, Linux distributions and Windows since Windows 10
  • ​Dropbear – SSH implementation for environments with low memory and processor resources, shipped in OpenWrt
  • ​PuTTY – SSH implementation for Windows, the client is commonly used but the use of the server is rarer
  • ​CopSSH – implementation of OpenSSH for Windows
SSH libraries (implementing server-side):
  • ​libssh – multiplatform C library implementing the SSHv2 protocol with bindings in Python, Perl and R; it’s used by KDE for sftp and by GitHub for the git SSH infrastructure
  • ​wolfSSH – SSHv2 server library written in ANSI C and targeted for embedded, RTOS, and resource-constrained environments
  • ​Apache MINA SSHD – Apache SSHD java library is based on Apache MINA
  • ​paramiko – Python SSHv2 protocol library


nc -vn <IP> 22

Automated ssh-audit

ssh-audit is a tool for ssh server & client configuration auditing.
  • SSH1 and SSH2 protocol server support;
  • analyze SSH client configuration;
  • grab banner, recognize device or software and operating system, detect compression;
  • gather key-exchange, host-key, encryption and message authentication code algorithms;
  • output algorithm information (available since, removed/disabled, unsafe/weak/legacy, etc);
  • output algorithm recommendations (append or remove based on recognized software version);
  • output security information (related issues, assigned CVE list, etc);
  • analyze SSH version compatibility based on algorithm information;
  • historical information from OpenSSH, Dropbear SSH and libssh;
  • runs on Linux and Windows;
  • no dependencies
usage: [-1246pbcnjvlt] <host>
-1, --ssh1 force ssh version 1 only
-2, --ssh2 force ssh version 2 only
-4, --ipv4 enable IPv4 (order of precedence)
-6, --ipv6 enable IPv6 (order of precedence)
-p, --port=<port> port to connect
-b, --batch batch output
-c, --client-audit starts a server on port 2222 to audit client
software config (use -p to change port;
use -t to change timeout)
-n, --no-colors disable colors
-j, --json JSON output
-v, --verbose verbose output
-l, --level=<level> minimum output level (info|warn|fail)
-t, --timeout=<secs> timeout (in seconds) for connection and reading
(default: 5)
$ python3 ssh-audit <IP>

Public SSH key of server

ssh-keyscan -t rsa <IP> -p <PORT>

Weak Cipher Algorithms

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

Nmap scripts

nmap -p22 <ip> -sC # Send default nmap scripts for SSH
nmap -p22 <ip> -sV # Retrieve version
nmap -p22 <ip> --script ssh2-enum-algos # Retrieve supported algorythms
nmap -p22 <ip> --script ssh-hostkey --script-args ssh_hostkey=full # Retrieve weak keys
nmap -p22 <ip> --script ssh-auth-methods --script-args="ssh.user=root" # Check authentication methods


  • ssh

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​

Some common ssh credentials here and here and below.

Private/Public Keys BF

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


crackmapexec using the ssh protocol can use the option --kerberos to authenticate via kerberos. For more info run crackmapexec ssh --help.

Default Credentials

apc, device
admin123, password, brocade, fibranne
admin, cisco, enable, hsa, pix, pnadmin, ripeop, root, shelladmin
admin, Admin123, default, password, secur4u, cisco, Cisco, _Cisco, cisco123, C1sco!23, Cisco123, Cisco1234, TANDBERG, change_it, 12345, ipics, pnadmin, diamond, hsadb, c, cc, attack, blender, changeme
root, nsroot, nsmaint, vdiadmin, kvm, cli, admin
C1trix321, nsroot, nsmaint, kaviza, kaviza123, freebsd, public, rootadmin, wanscaler
admin, user
private, admin, user
root, user1, admin, vkernel, cli
calvin, 123456, password, vkernel, Stor@ge!, admin
admin, root, sysadmin
EMCPMAdm7n, Password#1, Password123#, sysadmin, changeme, emc
admin, root, vcx, app, spvar, manage, hpsupport, opc_op
admin, password, hpinvent, iMC123, pvadmin, passw0rd, besgroup, vcx, nice, access, config, 3V@rpar, 3V#rpar, procurve, badg3r5, OpC_op, !manage, !admin
admin, root
123456, admin, root, Admin123, Admin@storage, Huawei12#$, HwDec@01, hwosta2.0, HuaWei123, fsp200@HW, huawei123
USERID, admin, manager, mqm, db2inst1, db2fenc1, dausr1, db2admin, iadmin, system, device, ufmcli, customer
PASSW0RD, passw0rd, admin, password, Passw8rd, iadmin, apc, 123456, cust0mer
root, oracle, oravis, applvis, ilom-admin, ilom-operator, nm2user
changeme, ilom-admin, ilom-operator, welcome1, oracle
vi-admin, root, hqadmin, vmware, admin
vmware, vmw@re, hqadmin, default

Config Misconfigurations

Root login

By default most SSH server implementation will allow root login, it is advised to disable it because if the credentials of this accounts leaks, attackers will get administrative privileges directly and this will also allow attackers to conduct bruteforce attacks on this account.
How to disable root login for openSSH:
  1. 1.
    Edit SSH server configuration sudoedit /etc/ssh/sshd_config
  2. 2.
    Change #PermitRootLogin yes into PermitRootLogin no
  3. 3.
    Take into account configuration changes: sudo systemctl daemon-reload
  4. 4.
    Restart the SSH server sudo systemctl restart sshd

SFTP command execution

Another common SSH misconfiguration is often seen in SFTP configuration. Most of the time when creating a SFTP server the administrator want users to have a SFTP access to share files but not to get a remote shell on the machine. So they think that creating a user, attributing him a placeholder shell (like /usr/bin/nologin or /usr/bin/false) and chrooting him in a jail is enough to avoid a shell access or abuse on the whole file system. But they are wrong, a user can ask to execute a command right after authentication before it’s default command or shell is executed. So to bypass the placeholder shell that will deny shell access, one only has to ask to execute a command (eg. /bin/bash) before, just by doing:
$ ssh -v [email protected] id
debug1: Authentication succeeded (keyboard-interactive).
Authenticated to ([]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: pledge: network
debug1: client_input_global_request: rtype [email protected] want_reply 0
debug1: Sending command: id
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype [email protected] reply 0
uid=1000(noraj) gid=100(users) groups=100(users)
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 2412, received 2480 bytes, in 0.1 seconds
Bytes per second: sent 43133.4, received 44349.5
debug1: Exit status 0
$ ssh [email protected] /bin/bash
Here is an example of secure SFTP configuration (/etc/ssh/sshd_config – openSSH) for the user noraj:
Match User noraj
ChrootDirectory %h
ForceCommand internal-sftp
AllowTcpForwarding no
PermitTunnel no
X11Forwarding no
PermitTTY no
This configuration will allow only SFTP: disabling shell access by forcing the start command and disabling TTY access but also disabling all kind of port forwarding or tunneling.

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>
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.

Authentication methods

On high security environment it’s a common practice to enable only key-based or two factor authentication rather than the simple factor password based authentication. But often the stronger authentication methods are enabled without disabling the weaker ones. A frequent case is enabling publickey on openSSH configuration and setting it as the default method but not disabling password. So by using the verbose mode of the SSH client an attacker can see that a weaker method is enabled:
$ ssh -v
OpenSSH_8.1p1, OpenSSL 1.1.1d 10 Sep 2019
debug1: Authentications that can continue: publickey,password,keyboard-interactive
For example if an authentication failure limit is set and you never get the chance to reach the password method, you can use the PreferredAuthentications option to force to use this method.
$ ssh -v -o PreferredAuthentications=password
debug1: Next authentication method: password
Review the SSH server configuration is necessary to check that only expected methods are authorized. Using the verbose mode on the client can help to see the effectiveness of the configuration.

Config files




HackTricks Automatic Commands

Protocol_Name: SSH
Port_Number: 22
Protocol_Description: Secure Shell Hardening
Name: Hydra Brute Force
Description: Need Username
Command: hydra -v -V -u -l {Username} -P {Big_Passwordlist} -t 1 -u {IP} ssh