Subdomain Enumeration

Maximum coverage. Multiple sources. Continuously updated.

When to invoke

Trigger phrases:

• "enumerate subdomains for X"
• "subfinder X"
• "find subdomains of target.com"
• "run full subdomain recon"

Pre-flight checklist

• Scope confirmed: *.target.com is in-scope (see [[scope-analysis]])
• OOS list ready (to filter results)
• API keys configured (see below)
• Output dir created: mkdir -p loot/<target>/subs/

API keys (set these once)

Most passive sources work without keys but with keys you 3-5x your coverage:

# ~/.config/subfinder/provider-config.yaml
chaos:
  - "YOUR_CHAOS_KEY"
binaryedge:
  - "YOUR_BINARYEDGE_KEY"
censys:
  - "ID:SECRET"
github:
  - "ghp_YOUR_GITHUB_TOKEN"
shodan:
  - "YOUR_SHODAN_KEY"
securitytrails:
  - "YOUR_SECURITYTRAILS_KEY"
virustotal:
  - "YOUR_VT_KEY"

Free tiers (sign up):

• Chaos: https://chaos.projectdiscovery.io (free for BB hunters)
• Censys: 250 queries/month free
• GitHub: any PAT works
• SecurityTrails: 50/month free
• VirusTotal: 4 req/min free

The full pipeline

1. Passive enumeration (no traffic to target)

TARGET="target.com"
OUT="loot/$TARGET/subs"
mkdir -p "$OUT"

# subfinder — fastest, broadest passive
subfinder -d "$TARGET" -all -recursive -silent > "$OUT/subfinder.txt"

# assetfinder — adds extra sources
assetfinder --subs-only "$TARGET" > "$OUT/assetfinder.txt"

# chaos — ProjectDiscovery's curated dataset
chaos -d "$TARGET" -silent > "$OUT/chaos.txt"

# crtsh — certificate transparency
curl -s "https://crt.sh/?q=%25.${TARGET}&output=json" | \
    jq -r '.[].name_value' | sed 's/\*\.//g' | sort -u > "$OUT/crtsh.txt"

# findomain — Rust-based, fast
findomain -t "$TARGET" -q > "$OUT/findomain.txt" 2>/dev/null

# github-subdomains — mines GitHub for subdomain mentions
# pip install github-subdomains (or use the Go tool)
github-subdomains -d "$TARGET" -t "$GITHUB_TOKEN" -o "$OUT/github.txt"

# Combine & dedupe
cat "$OUT"/*.txt | sort -u > "$OUT/passive.txt"
echo "[+] Passive sources: $(wc -l < "$OUT/passive.txt") unique subdomains"

2. Active enumeration (DNS brute force)

# Use a strong wordlist (assetnote wordlists are gold)
WORDLIST="$HOME/tools/assetnote-wordlists/data/manual/best-dns-wordlist.txt"

# puredns is the modern choice (fast, accurate)
# Install: go install github.com/d3mondev/puredns/v2@latest
puredns bruteforce "$WORDLIST" "$TARGET" \
    -r resolvers.txt \
    --rate-limit 1000 \
    --write "$OUT/bruteforce.txt"

# Alternative: shuffledns + dnsx
shuffledns -d "$TARGET" -w "$WORDLIST" -r resolvers.txt -mode bruteforce > "$OUT/shuffle.txt"

Get a fresh resolvers file (critical for speed):

# Resolvers — use trusted, fast ones
curl -s https://raw.githubusercontent.com/proabiral/Fresh-Resolvers/master/resolvers.txt > resolvers.txt
# Validate them
dnsvalidator -tL resolvers.txt -threads 200 -o validated-resolvers.txt

3. Permutation / alteration

# Combine known subs into permutations
gotator -sub "$OUT/passive.txt" -perm permutations.txt -depth 1 -numbers 5 | \
    puredns resolve --resolvers validated-resolvers.txt > "$OUT/permutations.txt"

# Alternative: dnsgen
cat "$OUT/passive.txt" | dnsgen - | puredns resolve --resolvers validated-resolvers.txt > "$OUT/dnsgen.txt"

4. Combine, dedupe, filter OOS

# Everything in one file
cat "$OUT"/*.txt | sort -u > "$OUT/all.txt"

# Remove out-of-scope (from scope-analysis output)
grep -vFf "scope-oos.txt" "$OUT/all.txt" > "$OUT/in-scope.txt"

echo "[+] Total subdomains: $(wc -l < "$OUT/all.txt")"
echo "[+] In-scope:         $(wc -l < "$OUT/in-scope.txt")"

5. Hand off to next skill

The output $OUT/in-scope.txt feeds directly into [[asset-discovery]].

One-liner full pipeline

# Save this as scripts/full-sub-recon.sh
TARGET=$1
OUT="loot/$TARGET/subs"
mkdir -p "$OUT"

(subfinder -d "$TARGET" -all -silent;
 assetfinder --subs-only "$TARGET";
 chaos -d "$TARGET" -silent;
 curl -s "https://crt.sh/?q=%25.${TARGET}&output=json" | jq -r '.[].name_value' | sed 's/\*\.//g';
 findomain -t "$TARGET" -q 2>/dev/null) | sort -u | anew "$OUT/passive.txt"

echo "[+] Passive done: $(wc -l < "$OUT/passive.txt") subs"

Run:

chmod +x scripts/full-sub-recon.sh
./scripts/full-sub-recon.sh target.com

Continuous mode

Set up nightly diff alerts → see [[continuous-monitoring]].

# In cron
0 3 * * * cd /home/user/bb && ./scripts/full-sub-recon.sh target.com && \
          diff -u loot/target.com/subs/yesterday.txt loot/target.com/subs/passive.txt | \
          grep '^+' | grep -v '^+++' | \
          notify -bulk -id discord

Output template

target.com
├── subs/
│   ├── passive.txt        ← passive sources
│   ├── bruteforce.txt     ← active DNS brute
│   ├── permutations.txt   ← gotator/dnsgen
│   ├── all.txt            ← combined+sorted
│   └── in-scope.txt       ← filtered against OOS
└── stats.txt
    ├── 247 total
    ├── 14 OOS removed
    └── 233 in-scope

Cross-references

• [[scope-analysis]] — gives you the OOS filter
• [[asset-discovery]] — next: which of these are alive?
• [[continuous-monitoring]] — nightly diff alerts
• [[subdomain-takeover]] — check for dangling DNS

Common pitfalls

1. No API keys = passive coverage drops ~70%. Configure Chaos minimum.
2. Bad resolvers = false positives. Validate with dnsvalidator.
3. Including OOS = wasted hunt time, possible report rejection.
4. One-shot enumeration = misses new subdomains added daily. Continuous is critical.
5. Trusting brute force alone = misses passive-only subs (like internal CDN names).

Anti-WAF / stealth tips

• Some programs have WAFs on *.target.com that rate-limit recon
• Throttle: --rate-limit 100 on puredns
• Use rotating User-Agents on HTTP-based sources (httpx)
• For private programs, ask the manager if there's a recon allowlist for your IP

Validation: did we cover everything?

Sanity checks:

• Number of subs > 10 for any non-trivial target?
• Did *.api.target.com show up if APIs exist?
• Are subdomain levels covered? (a.b.c.target.com)
• Did Wayback / waybackurls also reveal hostnames we missed?
  • cat all-urls-from-wayback.txt | unfurl domains | grep target.com | anew "$OUT/wayback-domains.txt"