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

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"