subdomain-enumeration

# Subdomain Enumeration Skill Comprehensive subdomain discovery using certificate transparency logs (crt.sh), DNS brute force, and passive sources. The first step in any recon pipeline — you can't attack what you don't know exists. Subdomain enumeration consistently reveals staging environments, internal admin panels, API gateways, and forgotten WordPress installs that are softer targets than the production site. ## When to Use - Starting recon on any target domain. - Production site is well-secured — find softer entry points. - After `skill_view(name='wp-mass-recon')` — enumerate subdomains for each WordPress target. - Building a complete asset inventory for a target organization. ## Prerequisites - `curl`, `httpx`, `dig`, `jq`, `dnsx`, and `subfinder`. - A DNS brute-force wordlist, supplied by the operator. - Approval to disclose the domain to third-party passive sources such as crt.sh, crt.name, and subfinder providers. ## How to Run ```bash DOMAIN="${1:-example.com}" OUTPUT_ROOT="${OUTPUT_DIR:-./output}" OUTDIR="$OUTPUT_ROOT/subdomains/$DOMAIN" if [[ ! "$DOMAIN" =~ ^[A-Za-z0-9.-]+$ ]]; then echo "Invalid domain: $DOMAIN" >&2 exit 2 fi mkdir -p "$OUTDIR" # Passive: crt.sh (retry: it frequently returns 502 while its database refreshes) for attempt in 1 2 3; do curl -fsS --max-time 30 --connect-timeout 10 \ "https://crt.sh/?q=%25.$DOMAIN&output=json" -o "$OUTDIR/crtsh_raw.json" && break sleep 15 done jq -r '.[].name_value' "$OUTDIR/crtsh_raw.json" 2>/dev/null \ | sed 's/\*\.//g' \ | sort -u > "$OUTDIR/crtsh.txt" # If crt.sh stays down, crtsh.txt ends up empty: keep going with crt.name/subfinder. # crt.name (historical CT data; resolve names before probing) curl -fsS --max-time 30 --connect-timeout 10 "https://crt.name/v1/search?apex=$DOMAIN" \ | sed 's/\r$//' \ | sed 's/^\*\.//' \ | sort -u > "$OUTDIR/crtname.txt" # Passive: subfinder subfinder -d "$DOMAIN" -silent -timeout 30 > "$OUTDIR/subfinder.txt" # Merge and deduplicate cat "$OUTDIR/crtsh.txt" "$OUTDIR/crtname.txt" "$OUTDIR/subfinder.txt" \ | grep -E '^[A-Za-z0-9.-]+\.[A-Za-z]{2,}$' \ | sort -u > "$OUTDIR/all_subs.txt" # Probe live hosts httpx -silent -l "$OUTDIR/all_subs.txt" -threads 50 -rate-limit 2 \ -status-code -tech-detect -title -o "$OUTDIR/alive.txt" ``` ## Quick Reference | Source | Method | Coverage | Speed | |--------|--------|----------|-------| | crt.sh | Certificate transparency | Excellent (most certs) | Fast (1-5s) | | subfinder | Passive APIs (VirusTotal, Shodan, DNSdumpster, etc.) | Very good | Fast (30-60s) | | dnsx | Bulk DNS A/AAAA/CNAME resolution (100x faster than dig) | Good (uncovers non-HTTP) | Fast (10-30s) | | httpx probe | Live HTTP/HTTPS check | Best for web attack surface | Fast (30-60s) | | Google dork | `site:example.com` | Supplemental | Manual | ## Procedure ### Step 1 — Passive Enumeration (crt.sh + subfinder) ```bash DOMAIN="$1" OUTPUT_ROOT="${OUTPUT_DIR:-./output}" OUTDIR="$OUTPUT_ROOT/subdomains/$DOMAIN" if [[ ! "$DOMAIN" =~ ^[A-Za-z0-9.-]+$ ]]; then echo "Invalid domain: $DOMAIN" >&2 exit 2 fi mkdir -p "$OUTDIR" echo "[*] Passive enumeration for $DOMAIN..." # crt.sh — certificate transparency logs (retry: it frequently returns 502 while its database refreshes) echo "[*] crt.sh query..." for attempt in 1 2 3; do curl -fsS --max-time 30 --connect-timeout 10 \ "https://crt.sh/?q=%25.$DOMAIN&output=json" -o "$OUTDIR/crtsh_raw.json" 2>/dev/null && break sleep 15 done jq -r '.[].name_value' "$OUTDIR/crtsh_raw.json" 2>/dev/null | \ sed 's/\*\.//g' | \ sed 's/^www\.//' | \ sort -u > "$OUTDIR/crtsh.txt" crt_count=$(wc -l < "$OUTDIR/crtsh.txt") echo " crt.sh: $crt_count entries" if [[ ! -s "$OUTDIR/crtsh.txt" ]]; then echo " [!] crt.sh unavailable or empty after retries; results are incomplete" >&2 fi # crt.name — historical certificate-transparency data echo "[*] crt.name query..." curl -fsS --max-time 30 --connect-timeout 10 "https://crt.name/v1/search?apex=$DOMAIN" 2>/dev/null | \ sed 's/\r$//' | \ sed 's/^\*\.//' | \ sort -u > "$OUTDIR/crtname.txt" crtname_count=$(wc -l < "$OUTDIR/crtname.txt") echo " crt.name: $crtname_count entries (historical; resolve before probing)" # Also query with %25. (wildcard) for attempt in 1 2 3; do curl -fsS --max-time 30 --connect-timeout 10 \ "https://crt.sh/?q=%25.%25.$DOMAIN&output=json" -o "$OUTDIR/crtsh_wildcard_raw.json" 2>/dev/null && break sleep 15 done jq -r '.[].name_value' "$OUTDIR/crtsh_wildcard_raw.json" 2>/dev/null | \ sed 's/\*\.//g' | \ sort -u > "$OUTDIR/crtsh_wildcard.txt" # subfinder — passive API aggregation echo "[*] subfinder..." subfinder -d "$DOMAIN" -silent -timeout 30 2>/dev/null | sort -u > "$OUTDIR/subfinder.txt" subf_count=$(wc -l < "$OUTDIR/subfinder.txt") echo " subfinder: $subf_count entries" # Merge all passive sources cat "$OUTDIR"/crtsh.txt "$OUTDIR"/crtsh_wildcard.txt "$OUTDIR"/crtname.txt "$OUTDIR"/subfinder.txt 2>/dev/null | \ sed 's/^www\.//' | \ grep -E '^[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$' | \ sort -u > "$OUTDIR/all_passive.txt" total=$(wc -l < "$OUTDIR/all_passive.txt") echo "" echo "[+] Total unique subdomains (passive): $total" ``` ### Step 2 — DNS Resolution ```bash DOMAIN="$1" OUTPUT_ROOT="${OUTPUT_DIR:-./output}" OUTDIR="$OUTPUT_ROOT/subdomains/$DOMAIN" echo "[*] Resolving subdomains..." # Batch resolve with dnsx (100x faster than dig loop) dnsx -silent -l "$OUTDIR/all_passive.txt" -a -resp-only -o "$OUTDIR/resolved_raw.txt" 2>/dev/null # Format output: subdomain => IP while read -r line; do sub=$(echo "$line" | cut -d' ' -f1) ip=$(echo "$line" | cut -d' ' -f2) echo "$sub => $ip" done < "$OUTDIR/resolved_raw.txt" > "$OUTDIR/resolved.txt" resolved=$(wc -l < "$OUTDIR/resolved.txt") echo "[+] $resolved subdomains resolved to IPs" # Count unique IPs unique_ips=$(awk '{print $3}' "$OUTDIR/resolved.txt" | sort -u | wc -l) echo "[+] $unique_ips unique IPs" # Identify shared hosting (many subdomains → same IP) echo "" echo "[*] Shared hosting clusters:" awk '{print $3}' "$OUTDIR/resolved.txt" | sort | uniq -c | sort -rn | head -10 | while read -r count ip; do [[ "$count" -gt 1 ]] && echo " $ip: $count subdomains" done ``` ### Step 3 — Live Host Discovery ```bash DOMAIN="$1" OUTPUT_ROOT="${OUTPUT_DIR:-./output}" OUTDIR="$OUTPUT_ROOT/subdomains/$DOMAIN" echo "[*] Probing live hosts..." # httpx with tech detection httpx -silent -l "$OUTDIR/all_passive.txt" -threads 50 \ -status-code -tech-detect -title -location \ -o "$OUTDIR/alive.txt" 2>/dev/null alive=$(wc -l < "$OUTDIR/alive.txt") echo "[+] $alive live hosts" # Categorize by status code echo "" echo "[*] By HTTP status:" echo " 200: $(grep -c '\[200\]' "$OUTDIR/alive.txt")" echo " 301/302: $(grep -cE '\[301\]|\[302\]' "$OUTDIR/alive.txt")" echo " 403: $(grep -c '\[403\]' "$OUTDIR/alive.txt")" echo " 404: $(grep -c '\[404\]' "$OUTDIR/alive.txt")" # Categorize by technology echo "" echo "[*] By technology:" grep -Eo '\[[a-z-]+\]' "$OUTDIR/alive.txt" | tr -d '[]' | sort | uniq -c | sort -rn | head -15 # WordPress subdomains echo "" echo "[*] WordPress subdomains:" grep -i 'wordpress' "$OUTDIR/alive.txt" | awk '{print $1}' | head -10 # Non-HTTP services (from DNS resolution) echo "" echo "[*] Interesting non-standard ports from DNS (MX, NS, etc.):" dig +short "$DOMAIN" MX 2>/dev/null | head -5 dig +short "$DOMAIN" NS 2>/dev/null | head -5 dig +short "$DOMAIN" TXT 2>/dev/null | grep -i 'spf\|v=spf' | head -3 ``` ### Step 4 — Subdomain Categorization ```bash DOMAIN="$1" OUTPUT_ROOT="${OUTPUT_DIR:-./output}" OUTDIR="$OUTPUT_ROOT/subdomains/$DOMAIN" echo "[*] Categorizing subdomains..." # Staging/Dev echo "" echo "=== STAGING / DEV ===" grep -iE 'staging|stage|dev\.|development|test|uat|beta|sandbox|preview|qa' "$OUTDIR/all_passive.txt" # Admin/Internal echo "" echo "=== ADMIN / INTERNAL ===" grep -iE 'admin|portal|internal|dashboard|manage|cp\.|control|panel|cpanel|webmail|mail\.' "$OUTDIR/all_passive.txt" # API echo "" echo "=== API ===" grep -iE 'api|rest|graphql|ws\.|websocket' "$OUTDIR/all_passive.txt" # Infrastructure echo "" echo "=== CDN / STATIC ===" grep -iE 'cdn|static|assets|media|img|images|files|download|origin|proxy' "$OUTDIR/all_passive.txt" # Email echo "" echo "=== EMAIL ===" grep -iE 'mail\.|smtp|imap|pop|email|webmail|autodiscover' "$OUTDIR/all_passive.txt" # Cloud echo "" echo "=== CLOUD ===" grep -iE 'aws|azure|gcp|cloud|s3|bucket|firebase' "$OUTDIR/all_passive.txt" # Legacy echo "" echo "=== LEGACY / OLD ===" grep -iE 'old|old\.|v1|v2|legacy|archive|backup|bak' "$OUTDIR/all_passive.txt" ``` ### Step 5 — Subdomain Takeover Check ```bash DOMAIN="$1"