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External Information Gathering

🎯 Overview

External Information Gathering is the critical first phase of enterprise network attacks. This process involves systematic reconnaissance to map the attack surface, identify services, discover subdomains, and gather intelligence for targeted exploitation against external-facing infrastructure.

🔍 Initial Network Reconnaissance

📊 Quick Port Discovery

# Initial top 1000 ports scan
sudo nmap --open -oA target_tcp_1k -iL scope

# Key findings analysis:
PORT     STATE SERVICE
21/tcp   open  ftp
22/tcp   open  ssh
25/tcp   open  smtp
53/tcp   open  domain
80/tcp   open  http
110/tcp  open  pop3
143/tcp  open  imap
993/tcp  open  imaps
995/tcp  open  pop3s
8080/tcp open  http-proxy

# Service categories identified:
- Web services (80, 8080)
- Email services (25, 110, 143, 993, 995)
- File transfer (21)
- Remote access (22)
- DNS services (53)

🔧 Comprehensive Service Enumeration

# Full port aggressive scan
sudo nmap --open -p- -A -oA target_tcp_all_svc -iL scope

# Key service discoveries:
21/tcp   open  ftp      vsftpd 3.0.3
22/tcp   open  ssh      OpenSSH 8.2p1 Ubuntu 4ubuntu0.5
25/tcp   open  smtp     Postfix smtpd
53/tcp   open  domain   (unknown banner: 1337_HTB_DNS)
80/tcp   open  http     Apache httpd 2.4.41 ((Ubuntu))
8080/tcp open  http     Apache httpd 2.4.41 ((Ubuntu))

# Anonymous FTP access discovered:
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
|_-rw-r--r--    1 0        0              38 May 30 17:16 flag.txt

📈 Service Analysis with Nmap Grep

# Extract service information efficiently
egrep -v "^#|Status: Up" target_tcp_all_svc.gnmap | cut -d ' ' -f4- | tr ',' '\n' | \
sed -e 's/^[ \t]*//' | awk -F '/' '{print $7}' | grep -v "^$" | sort | uniq -c | sort -k 1 -nr

# Results:
      2 Dovecot pop3d
      2 Dovecot imapd (Ubuntu)
      2 Apache httpd 2.4.41 ((Ubuntu))
      1 vsftpd 3.0.3
      1 Postfix smtpd
      1 OpenSSH 8.2p1 Ubuntu 4ubuntu0.5
      1 2-4 (RPC #100000)

🌐 DNS Enumeration

📋 DNS Zone Transfer Attack

# Attempt zone transfer for subdomain discovery
dig axfr inlanefreight.local @TARGET_IP

# Successful zone transfer results:
inlanefreight.local.     86400  IN  SOA   ns1.inlanfreight.local. dnsadmin.inlanefreight.local.
blog.inlanefreight.local.     86400  IN  A    127.0.0.1
careers.inlanefreight.local.  86400  IN  A    127.0.0.1
dev.inlanefreight.local.      86400  IN  A    127.0.0.1
flag.inlanefreight.local.     86400  IN  TXT  "HTB{..."
gitlab.inlanefreight.local.   86400  IN  A    127.0.0.1
ir.inlanefreight.local.       86400  IN  A    127.0.0.1
status.inlanefreight.local.   86400  IN  A    127.0.0.1
support.inlanefreight.local.  86400  IN  A    127.0.0.1
tracking.inlanefreight.local. 86400  IN  A    127.0.0.1
vpn.inlanefreight.local.      86400  IN  A    127.0.0.1

# Discovery: 9 additional subdomains + flag in TXT record

🔍 Alternative DNS Enumeration

# If zone transfer fails, use passive methods:
# - DNSDumpster.com
# - Certificate transparency logs
# - Search engine dorking
# - Subdomain brute forcing

# Active subdomain enumeration:
ffuf -w /opt/useful/seclists/Discovery/DNS/subdomains-top1million-5000.txt:FUZZ -u http://FUZZ.inlanefreight.local

🌐 Virtual Host Discovery

📊 VHost Enumeration Process

# Step 1: Determine invalid vhost response size
curl -s -I http://TARGET_IP -H "HOST: defnotvalid.inlanefreight.local" | grep "Content-Length:"
# Result: Content-Length: 15157

# Step 2: Fuzz vhosts filtering invalid responses
ffuf -w /opt/useful/seclists/Discovery/DNS/namelist.txt:FUZZ -u http://TARGET_IP/ -H 'Host:FUZZ.inlanefreight.local' -fs 15157

# Results discovered:
blog                    [Status: 200, Size: 8708]
careers                 [Status: 200, Size: 51810]
dev                     [Status: 200, Size: 2048]
gitlab                  [Status: 302, Size: 113]
ir                      [Status: 200, Size: 28545]
monitoring              [Status: 200, Size: 56]    # ← Additional vhost not in DNS
status                  [Status: 200, Size: 917]
support                 [Status: 200, Size: 26635]
tracking                [Status: 200, Size: 35185]
vpn                     [Status: 200, Size: 1578]

🔧 Alternative VHost Tools

# Gobuster vhost enumeration
gobuster vhost -u http://TARGET_IP -w /opt/useful/seclists/Discovery/DNS/subdomains-top1million-5000.txt --domain inlanefreight.local

# Wfuzz vhost discovery
wfuzz -c -f sub-fighter -w /opt/useful/seclists/Discovery/DNS/namelist.txt -u "http://TARGET_IP" -H "Host: FUZZ.inlanefreight.local" --hh 15157

📝 Host File Configuration

🔧 Adding Discovered Hosts

# Add all discovered subdomains to /etc/hosts
sudo tee -a /etc/hosts > /dev/null <<EOT

## inlanefreight hosts 
TARGET_IP inlanefreight.local blog.inlanefreight.local careers.inlanefreight.local dev.inlanefreight.local gitlab.inlanefreight.local ir.inlanefreight.local status.inlanefreight.local support.inlanefreight.local tracking.inlanefreight.local vpn.inlanefreight.local monitoring.inlanefreight.local
EOT

# Verify configuration
cat /etc/hosts | grep inlanefreight

🎯 HTB Academy Lab Solutions

Lab Environment

# Target: 10.129.211.225 (ACADEMY-AEN-DMZ01)
# Add to /etc/hosts:
sudo sh -c 'echo "TARGET_IP inlanefreight.local" >> /etc/hosts'

🔍 Question 1: Banner Grab Non-Standard Service

# Service enumeration with version detection
sudo nmap -sC -sV inlanefreight.local

# Key finding in DNS service:
53/tcp   open  domain   (unknown banner: 1337_HTB_DNS)
| dns-nsid:
|_  bind.version: 1337_HTB_DNS

# Answer: 1337_HTB_DNS

🌐 Question 2: DNS Zone Transfer Flag

# Perform zone transfer
dig AXFR inlanefreight.local @TARGET_IP

# Flag discovered in TXT record:
flag.inlanefreight.local. 86400  IN  TXT  "HTB{..."

# Answer: HTB{DNs_ZOn3_Tr@nsf3r}

📍 Question 3: Flag Subdomain FQDN

# From zone transfer output:
flag.inlanefreight.local. 86400  IN  TXT  "HTB{..."

# Answer: flag.inlanefreight.local

🔍 Question 4: Additional VHost Discovery

# Determine invalid response size
curl -sI http://TARGET_IP/ -H "Host: defnotvalid.inlanefreight.local" | grep "Content-Length:"
# Result: Content-Length: 15157

# Fuzz for additional vhosts
ffuf -s -w /opt/useful/SecLists/Discovery/DNS/namelist.txt:FUZZ -u http://TARGET_IP/ -H 'Host: FUZZ.inlanefreight.local' -fs 15157

# Additional vhost found:
monitoring              [Status: 200, Size: 56]

# Answer: monitoring

🔄 Information Gathering Workflow

📊 Systematic Approach

# 1. Initial port discovery
sudo nmap --open -oA quick_scan -iL scope

# 2. Service enumeration
sudo nmap --open -p- -A -oA full_scan -iL scope

# 3. DNS zone transfer attempt
dig axfr DOMAIN @TARGET_IP

# 4. Subdomain/vhost discovery
ffuf -w wordlist -u http://TARGET/ -H 'Host:FUZZ.domain' -fs INVALID_SIZE

# 5. Host file configuration
sudo tee -a /etc/hosts <<< "TARGET_IP domain subdomain1.domain subdomain2.domain"

# 6. Service-specific enumeration
# Continue with FTP, HTTP, SMTP, etc. detailed analysis

🎯 Attack Surface Mapping

# Service categorization:
Web Services:     80, 443, 8080, 8443
Email Services:   25, 110, 143, 587, 993, 995
File Transfer:    21, 22, 69, 873
Database:         1433, 3306, 5432, 1521
Management:       161, 623, 8080, 9090
Remote Access:    22, 23, 3389, 5985, 5986

# Priority targets:
1. Web applications (immediate attack surface)
2. Anonymous/weak authentication services
3. Known vulnerable service versions
4. Management interfaces
5. Email services for user enumeration

⚠️ Reconnaissance Best Practices

🔒 Stealth Considerations

# Timing controls for stealth
nmap -T2 --scan-delay 5s TARGET_IP

# Fragmented packets
nmap -f TARGET_IP

# Source port spoofing
nmap --source-port 53 TARGET_IP

# Decoy scanning
nmap -D RND:10 TARGET_IP

📋 Documentation Standards

# Essential documentation:
- All scan outputs saved with timestamps
- Service version information recorded
- Subdomain/vhost discovery results
- Anonymous access findings
- Potential attack vectors identified
- Evidence screenshots for findings

💡 Key Takeaways

  1. Systematic enumeration reveals complete attack surface
  2. DNS zone transfers provide valuable subdomain intelligence
  3. VHost discovery uncovers hidden applications
  4. Service versioning enables vulnerability research
  5. Anonymous access often provides immediate foothold opportunities
  6. Comprehensive documentation essential for attack planning
  7. Multiple enumeration methods ensure complete coverage

External information gathering establishes the foundation for enterprise network attacks by mapping the complete external attack surface and identifying high-value targets for exploitation.