subdomain-enum

name	subdomain-enum
description	Enumerate subdomains for a target domain using passive and active reconnaissance techniques. Use when starting reconnaissance on a new target, when you need to discover the attack surface, when expanding scope from a root domain, or when the user provides a domain to investigate.
tags	["security","subdomain","enumeration","dns","reconnaissance"]
triggers	["subdomain enumeration","find subdomains","subdomain scan","subdomain discovery"]

subdomain-enum

When to Use

• Starting reconnaissance on a new target domain
• Need to discover all subdomains for attack surface mapping
• Expanding scope from a single root domain
• User provides a domain and asks about subdomains
• Building initial target list for vulnerability scanning
• Need to find hidden or forgotten subdomains
• Preparing for web application testing
• Asset discovery phase of bug bounty hunting

Quick Start

# Fast passive enumeration with subfinder
subfinder -d example.com -silent -o subdomains.txt

# Validate live subdomains with httpx
cat subdomains.txt | httpx -silent -o live_subdomains.txt

Step-by-Step Process

Phase 1: Fast Passive Enumeration (Subfinder)

1. Basic enumeration:

   subfinder -d example.com -o subfinder_results.txt
   

2. Silent mode for clean output:

   subfinder -d example.com -silent -o subdomains.txt
   

3. Use all sources (comprehensive):

   subfinder -d example.com -all -o subdomains_all.txt
   

4. JSON output:

   subfinder -d example.com -silent -oJ -o subdomains.json
   

5. Multiple domains from file:

   subfinder -dL domains.txt -o all_subdomains.txt
   

6. Recursive enumeration:

   subfinder -d example.com -recursive -o recursive_subs.txt
   

Phase 2: Deep Enumeration (Amass)

1. Passive only:

   amass enum -passive -d example.com -o amass_passive.txt
   

2. Active enumeration:

   amass enum -active -d example.com -o amass_active.txt
   

3. With brute forcing:

   amass enum -brute -d example.com -o amass_brute.txt
   

4. JSON output:

   amass enum -d example.com -json amass_results.json
   

Phase 3: Validation (Httpx)

1. Basic probe:

   cat subdomains.txt | httpx -silent -o live_hosts.txt
   

2. With status codes:

   cat subdomains.txt | httpx -silent -sc -o live_with_status.txt
   

3. Full information:

   cat subdomains.txt | httpx -silent -sc -title -td -o detailed_hosts.txt
   

4. JSON output:

   cat subdomains.txt | httpx -silent -json -o httpx_results.json
   

5. With technology detection:

   cat subdomains.txt | httpx -silent -td -json -o tech_results.json
   

Phase 4: Combine Results

cat subfinder_results.txt amass_passive.txt | sort -u > all_subdomains.txt

Examples

Example 1: Quick Bug Bounty Recon

Scenario: Fast subdomain discovery for a bug bounty target

subfinder -d hackerone.com -silent -o subs.txt
cat subs.txt | httpx -silent -sc -title

Output:

https://www.hackerone.com [200] [HackerOne | Bug Bounty Platform]
https://api.hackerone.com [401] [Unauthorized]
https://docs.hackerone.com [200] [HackerOne Platform Documentation]
https://support.hackerone.com [200] [HackerOne]

Example 2: Comprehensive Enumeration

Scenario: Thorough discovery with multiple tools

# Fast scan
subfinder -d target.com -all -o subfinder.txt

# Deep scan
amass enum -passive -d target.com -o amass.txt

# Combine
cat subfinder.txt amass.txt | sort -u > all_subs.txt

# Validate
cat all_subs.txt | httpx -silent -sc -title -td -json -o final.json

Example 3: Recursive Discovery

Scenario: Find sub-subdomains

subfinder -d example.com -recursive -o recursive.txt

Output:

api.example.com
dev.api.example.com
staging.api.example.com
internal.corp.example.com

Example 4: JSON Pipeline

Scenario: Structured output for processing

subfinder -d example.com -silent -oJ -o subs.json
cat subs.json | jq -r '.host' | httpx -silent -json -o httpx.json
cat httpx.json | jq -r 'select(.status_code == 200) | .url'

Example 5: Filter Interesting Targets

Scenario: Find high-value subdomains

subfinder -d target.com -silent -o subs.txt
grep -iE "(admin|dev|staging|test|api|internal|jenkins|jira)" subs.txt > interesting.txt
cat interesting.txt | httpx -silent -sc -title

Output:

https://admin.target.com [403] [Forbidden]
https://dev.target.com [200] [Development Environment]
https://jenkins.target.com [200] [Jenkins]

Example 6: Rate-Limited Scan

Scenario: Avoid detection

subfinder -d target.com -rl 5 -t 2 -o subs.txt
cat subs.txt | httpx -silent -rl 10 -t 25 -o live.txt

Example 7: Technology-Focused

Scenario: Find specific tech stacks

subfinder -d example.com -silent | httpx -silent -td -json -o tech.json
cat tech.json | jq 'select(.tech | contains(["WordPress"]))'

Error Handling

Error	Cause	Resolution
no results found	No indexed subdomains	Try amass brute force
context deadline exceeded	Timeout	Increase -timeout
rate limit exceeded	Too many requests	Use -rl flag
could not resolve host	DNS failure	Check resolvers
no sources configured	Missing API keys	Configure provider-config.yaml
connection refused	Blocked	Use rate limiting
too many open files	Resource limit	Reduce -t threads

Tool Reference

Subfinder Flags

Flag	Description
-d, -domain	Target domain
-dL, -list	File with domains
-all	Use all sources
-recursive	Recursive enumeration
-o, -output	Output file
-oJ, -json	JSON output
-silent	Clean output
-rl, -rate-limit	Requests per second
-t	Concurrent threads
-timeout	Timeout seconds
-r, -resolvers	Custom resolvers
-nW, -active	Active subdomains only
-config	Config file path
-pc, -provider-config	API keys config

Amass Flags

Flag	Description
-d	Target domain
-passive	Passive only
-active	Include active
-brute	Enable brute force
-o	Output file
-json	JSON output
-config	Config file
-w	Wordlist for brute

Httpx Flags

Flag	Description
-l, -list	Input file
-sc, -status-code	Show status code
-title	Show page title
-td, -tech-detect	Detect technologies
-ip	Show IP address
-cdn	Show CDN detection
-o, -output	Output file
-json	JSON output
-silent	Clean output
-mc, -match-code	Match status codes
-fc, -filter-code	Filter status codes
-t, -threads	Thread count
-rl, -rate-limit	Requests per second

Advanced Techniques

Wildcard Detection

# Check for wildcard
dig randomnonexistent123456.example.com +short

# Filter wildcards
subfinder -d example.com -nW -o filtered.txt

Certificate Transparency

# Query CT logs directly
curl -s "https://crt.sh/?q=%25.example.com&output=json" | jq -r '.[].name_value' | sort -u

ASN Discovery

# Find domains by ASN
amass intel -asn 12345 -o asn_domains.txt

Continuous Monitoring

# Baseline
subfinder -d example.com -silent -o baseline.txt

# Check for new
subfinder -d example.com -silent -o current.txt
diff baseline.txt current.txt > new_subs.txt

API Key Configuration

Subfinder (~/.config/subfinder/provider-config.yaml)

binaryedge:
  - your_api_key
censys:
  - your_api_id:your_api_secret
chaos:
  - your_api_key
github:
  - your_github_token
securitytrails:
  - your_api_key
shodan:
  - your_api_key
virustotal:
  - your_api_key

Amass (~/.config/amass/config.yaml)

datasources:
  SecurityTrails:
    apikey: your_api_key
  Shodan:
    apikey: your_api_key
  VirusTotal:
    apikey: your_api_key

Best Practices

Recommended Workflow

1. Start with subfinder - Fast, passive, low noise
2. Run amass passive - Additional sources
3. Run amass active - DNS brute forcing (if allowed)
4. Combine and deduplicate - Merge all results
5. Validate with httpx - Find live hosts
6. Filter interesting - Focus on valuable targets

Performance Tips

• Use -silent for cleaner pipeline output
• Set -rl rate limits for large domains
• Use -json for programmatic processing
• Run subfinder first (faster), then amass (thorough)
• Increase timeouts for slow networks
• Use custom resolvers for better DNS resolution

Common Wordlists

Wordlist	Size	Use Case
subdomains-top1million-5000.txt	5K	Quick
subdomains-top1million-20000.txt	20K	Standard
dns-Jhaddix.txt	2.2M	Comprehensive

Output Interpretation

Subfinder JSON Output

{
  "host": "api.example.com",
  "input": "example.com",
  "source": "alienvault"
}

Field	Description
host	Discovered subdomain
input	Original target domain
source	Data source that found it

Httpx JSON Output

{
  "timestamp": "2024-01-15T10:30:00.000Z",
  "url": "https://api.example.com",
  "input": "api.example.com",
  "status_code": 200,
  "title": "API Documentation",
  "webserver": "nginx/1.18.0",
  "tech": ["nginx", "PHP"],
  "content_length": 12345,
  "host": "93.184.216.34",
  "port": "443",
  "scheme": "https"
}

Field	Description
url	Full URL of the host
status_code	HTTP response code
title	HTML page title
webserver	Server header value
tech	Detected technologies
content_length	Response size
host	IP address

Status Code Meanings

Code	Meaning	Interest Level
200	OK	High - Active site
301/302	Redirect	Medium - Check destination
401	Unauthorized	High - Protected resource
403	Forbidden	High - Hidden content
404	Not Found	Low - May not exist
500	Server Error	Medium - Misconfigured
502/503	Gateway Error	Medium - Backend issues

Integration Examples

Pipe to Nuclei

subfinder -d example.com -silent | httpx -silent | nuclei -t cves/

Pipe to Katana

subfinder -d example.com -silent | httpx -silent | katana -silent

Pipe to Naabu

subfinder -d example.com -silent | naabu -silent -top-ports 100

Full Recon Pipeline

# Complete subdomain enumeration pipeline
TARGET="example.com"
OUTDIR="recon/${TARGET}"
mkdir -p "$OUTDIR"

# Enumerate
subfinder -d "$TARGET" -all -o "$OUTDIR/subfinder.txt"
amass enum -passive -d "$TARGET" -o "$OUTDIR/amass.txt"

# Combine and dedupe
cat "$OUTDIR"/*.txt | sort -u > "$OUTDIR/all_subs.txt"

# Validate and fingerprint
cat "$OUTDIR/all_subs.txt" | httpx -silent -sc -title -td -json -o "$OUTDIR/live.json"

# Summary
echo "Found $(wc -l < $OUTDIR/all_subs.txt) subdomains"
echo "Live hosts: $(wc -l < $OUTDIR/live.json)"

References

• Subfinder | Amass | Httpx | SecLists DNS