Subflare – Modern Subdomain Recon Tool

Fast passive recon + reliable DNS validation + automation-friendly output
Built for practical offensive security and defensive asset discovery workflows.

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╚══════╝ ╚═════╝ ╚═════╝ ╚═╝     ╚══════╝╚═╝  ╚═╝╚═╝  ╚═╝╚══════╝

        @sakibulalikhan
    Hiddeninvestigations.Net

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⚠️ Legal & Ethical Disclaimer

Subflare is provided for authorized security testing and asset discovery only.

• Use this tool only on:
  • infrastructure you own, or
  • targets where you have explicit written permission.
• Do not run unauthorized scans against third-party systems.
• The authors and Hidden Investigations are not responsible for misuse.

By using this project, you agree to follow all applicable laws and regulations.

---

Features

• ⚡ High-speed passive recon across 25 integrated sources
• 🧠 Source runtime controls: retries, backoff, rate limits, per-source timeout
• 🗂️ Passive cache layer + persistent cache index for faster reruns on large scopes
• 🔁 Recursive bruteforce + smart permutations for deeper host expansion
• 🌐 DNS validation pipeline with resolver health scoring
• 🚀 Pluggable DNS backend (standard or massdns)
• 🔎 Reverse DNS expansion to discover additional in-scope hosts
• 🧹 Wildcard filtering + trusted-resolver revalidation
• 🛰️ Infrastructure enrichment with ASN/CDN hints (--enrich-infra)
• 🌍 HTTP probe handoff (status, title, basic technology hints)
• 🛡️ Takeover signal checks with confidence scoring (low/medium/high)
• 🔄 Fingerprint update mode (--update-fingerprints) for takeover rules
• 🎯 Takeover-only mode for checking existing subdomain lists (--takeover)
• ⚙️ Adaptive concurrency (--auto-tune) based on observed failure rate
• 🧾 Production-friendly CLI UX with structured summary, result, and takeover sections
• 📊 Readable scan summary for operator workflow
• 🤖 Automation mode with strict stdout-only output
• 🧪 Workflow commands:
  • bench for throughput benchmarking
  • diff for old/new result comparison
  • monitor for scheduled recon and webhook alerts

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Requirements

• Go 1.23+
• Network connectivity for passive source APIs and DNS
• Optional API keys for premium providers (recommended)

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Installation

Option 1: Install with Go (recommended)

go install -v github.com/SecurityTalent/subflare/cmd/subflare@latest

Then run:

subflare --help

Option 2: Build from source

1. Clone repository:

git clone https://github.com/SecurityTalent/subflare.git
cd subflare

2. Build binary:

go mod tidy
go build -o subflare ./cmd/subflare

3. Verify:

subflare --help

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Usage

Basic run:

subflare -d example.com

With selected sources:

subflare -d example.com --sources crtsh,anubis,securitytrails

Automation-safe output:

cat domains.txt | subflare --stdin --strict-io --no-banner

Regex-based host reduction after DNS validation:

subflare -d example.com \
  --match-regex '^admin\.' \
  --match-regex '(dev|stage|staging)' \
  --exclude-regex '.*internal.*'

---

Commands

Command	Description
subflare	Run scan pipeline
subflare bench	Benchmark passive + resolver throughput
subflare diff	Compare old/new output files
subflare monitor	Scheduled scans + delta alerting

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Command Line Options

Core target & mode options

Option	Description	Default
-d, --domain	Target root domain	required unless --stdin, -l, --takeover, or --update-fingerprints
-l, --list	Input list file (domains/subdomains)	none
--takeover	Run takeover-only mode on provided hosts	false
--update-fingerprints	Update takeover fingerprint pack (and continue/exit)	false
--match-regex	Include validated hosts matching RE2 regex; repeatable	none
--exclude-regex	Exclude validated hosts matching RE2 regex; repeatable	none
--match-regex-file	Load include regex rules from file	none
--exclude-regex-file	Load exclude regex rules from file	none
--passive	Enable passive collection	true
--bruteforce	Enable bruteforce mode	false
-w, --wordlist	Bruteforce wordlist path	none
--bruteforce-depth	Recursive bruteforce label depth	1
--bruteforce-max	Max bruteforce candidates	10000
--permutation	Enable smart permutation expansion	false
--permutation-depth	Permutation recursion depth	1
--permutation-max	Max permutation candidates	5000
-s, --sources	Comma-separated source list	all
-es, --exclude-sources	Exclude source list	none
--list-sources	Print passive sources and exit	off
--provider-config	Provider env file path	~/.config/subflare/providers.env
--no-banner	Disable banner output	off

Passive runtime options

Option	Description	Default
--rate-limit	Global source request rate (req/sec)	0 (unlimited)
--rls	Per-source rate limits	none
--source-timeout	Source request timeout	20s
--source-timeout-source	Per-source timeout overrides	none
--source-retries	Retries per source	2
--source-backoff	Base retry backoff	300ms
--source-max-backoff	Max retry backoff	5s
--cache-dir	Passive cache directory	~/.cache/subflare
--cache-ttl	Passive cache TTL	24h
--no-cache	Disable passive cache	off
--auto-tune	Adaptive concurrency by timeout/error rate	off

DNS validation options

Option	Description	Default
-r, --resolvers	Fast resolver list/file	built-in
-tr, --trusted-resolvers	Trusted resolver list/file	built-in
-t, --threads	DNS worker concurrency	200
--dns-backend	DNS backend (standard or massdns)	standard
--massdns-path	Path to massdns binary	massdns
--rdns-expand	Expand via reverse DNS of resolved IPs	false
--rdns-limit	Max reverse-DNS expansion candidates	1000
--timeout	Per-query DNS timeout	3s
--retries	DNS retries per host	2
--wildcard-tests	Random suffix checks for wildcard detect	2

Regex filtering options

Option	Description	Default
--match-regex	Include validated hosts matching RE2 regex; repeatable or comma-separated	none
--exclude-regex	Exclude validated hosts matching RE2 regex; repeatable or comma-separated	none
--match-regex-file	File with include regex rules; ignores blank lines and # comments	none
--exclude-regex-file	File with exclude regex rules; ignores blank lines and # comments	none

Enrichment & takeover options

Option	Description	Default
--takeover	Run takeover-only mode on provided hosts	false
-l, --list	Input list file for takeover-only target hosts	none
--enrich-infra	Enrich validated hosts with ASN/CDN hints	false
--http-probe	Probe validated hosts over HTTP/HTTPS	false
--http-probe-timeout	Timeout for HTTP probe requests	5s
--http-probe-threads	Concurrency for HTTP probing	50
--takeover-check	Run takeover signal checks	false
--takeover-threads	Concurrency for takeover checks	25
--takeover-timeout	Timeout for takeover checks	5s

Output & automation options

Option	Description	Default
-o, --output	Save text output file	none
--jsonl	Save JSONL output file	none
--silent	Print only subdomains to stdout	off
--verbose	Show detailed source warnings	off
--stdin	Read domains from stdin	off
--strict-io	No banner/stats, stdout-only result mode	off

Monitor & webhook options

Option	Description	Default
--monitor-interval	Monitor interval	10m
--monitor-cycles	Number of cycles (0 infinite)	0
--only-new	Monitor mode stdout: print only newly discovered hosts	off
--state-dir	Snapshot state directory	tool default (falls back to /tmp/subflare-state when default is not writable)
--webhook	Generic webhook URL list	none
--webhook-discord	Discord webhook URL	none
--webhook-slack	Slack webhook URL	none
--webhook-telegram-bot	Telegram bot token	none
--webhook-telegram-chat	Telegram chat ID	none
--webhook-timeout	Webhook request timeout	10s

---

Passive Sources

Standard + public sources

• alienvault
• anubis
• certspotter
• commoncrawl
• crtsh
• digitorus
• hackertarget
• leakix
• rapiddns
• riddler
• sitedossier
• threatcrowd
• threatminer
• waybackarchive

API-driven enrichment sources

• censys
• chaos
• fofa
• github
• gitlab
• netlas
• securitytrails
• shodan
• virustotal
• whoisxmlapi
• zoomeyeapi

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Provider Keys

Default provider file path:

~/.config/subflare/providers.env

Custom path:

subflare -d example.com --provider-config /path/to/providers.env

Example:

SHODAN_API_KEY=...
SECURITYTRAILS_API_KEY=...
VIRUSTOTAL_API_KEY=...
CENSYS_API_ID=...
CENSYS_API_SECRET=...
WHOISXMLAPI_API_KEY=...
CHAOS_API_KEY=...
FOFA_EMAIL=...
FOFA_KEY=...
ZOOMEYE_API_KEY=...
GITHUB_TOKEN=...
GITLAB_TOKEN=...
NETLAS_API_KEY=...
CERTSPOTTER_TOKEN=...
LEAKIX_API_KEY=...
ALIENVAULT_API_KEY=...

---

Examples

Basic scan:

subflare -d hiddeninvestigations.net

Bruteforce + permutation depth tuning:

subflare -d hiddeninvestigations.net \
  --bruteforce -w words.txt \
  --bruteforce-depth 2 --bruteforce-max 20000 \
  --permutation --permutation-depth 2 --permutation-max 5000

MassDNS backend:

subflare -d hiddeninvestigations.net --dns-backend massdns --massdns-path /usr/bin/massdns

Reverse-DNS + HTTP probe + takeover checks:

subflare -d hiddeninvestigations.net --rdns-expand --http-probe --takeover-check

Regex include/exclude filtering:

subflare -d hiddeninvestigations.net \
  --match-regex '^admin\.' \
  --match-regex '(dev|stage|staging)' \
  --exclude-regex '.*internal.*'

Regex file-driven triage:

subflare -d hiddeninvestigations.net \
  --match-regex-file examples/regex/include-high-value.txt \
  --exclude-regex-file examples/regex/exclude-noise.txt \
  --jsonl results.jsonl

Infra enrichment + adaptive concurrency:

subflare -d hiddeninvestigations.net --enrich-infra --auto-tune

Takeover-only from file:

subflare --takeover -l subs.txt

Takeover-only from stdin:

cat sub.txt | subflare --takeover

Combine list file + stdin in automation mode:

subflare --stdin --strict-io --no-banner -l domain.txt

Update takeover fingerprints:

subflare --update-fingerprints

Save text + JSONL:

subflare -d hiddeninvestigations.net -o results.txt --jsonl results.jsonl

Show detailed source errors:

subflare -d hiddeninvestigations.net --verbose

Diff old and new runs:

subflare diff --old old.txt --new new.txt --show all

Monitor with Discord alerts:

subflare monitor -d hiddeninvestigations.net \
  --monitor-interval 30m \
  --state-dir /tmp/subflare-state \
  --webhook-discord 'https://discord.com/api/webhooks/...'

Monitor pipelines with only-new stdout:

subflare monitor -d hiddeninvestigations.net --only-new --strict-io

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Takeover Check Behavior

--takeover-check performs signal-based takeover checks on validated hosts:

• Matches known CNAME provider fingerprints.
• Flags dangling CNAME targets only when DNS errors indicate hard non-existence (for example NXDOMAIN / no such host).
• Applies provider-aware HTTP fingerprint checks using response status + content indicators.

Current built-in provider rules include:

• GitHub Pages
• Heroku
• ReadTheDocs
• Pantheon
• AWS S3 website/bucket endpoints
• Azure App Service
• Vercel
• Surge

--update-fingerprints refreshes the local fingerprint pack at:

~/.config/subflare/takeover-fingerprints.json

Scan summary now reports:

• takeover checked: how many hosts were evaluated for takeover signals.
• takeover signals: how many hosts matched takeover indicators.

When --takeover-check is enabled, terminal output also prints a dedicated Takeover Assessment section:

• Lists only hosts with takeover possibility signals ([TAKEOVER][HIGH|MEDIUM|LOW] ...)
• Prints a clear no-findings message (no luck) when no takeover possibility is detected
• Does not change the normal subdomain host result output format

This output is a high-value triage signal, not a final vulnerability verdict. Always manually verify takeover candidates before reporting.

--takeover runs takeover checks directly on provided host lists (-l, --stdin, or piped stdin) without running passive/bruteforce discovery.

With --takeover --strict-io, stdout contains only takeover-positive hosts.

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Regex Filtering

Regex filters are applied only after trusted DNS validation. This keeps discovery behavior intact while reducing noise before HTTP probing, infrastructure enrichment, takeover checks, and final text or JSONL output.

• Include rules from --match-regex and --match-regex-file are OR-matched.
• Exclude rules from --exclude-regex and --exclude-regex-file are OR-matched.
• Blank lines and # comment lines are ignored in rule files.
• Invalid regex patterns are skipped as non-fatal warnings; scans continue.
• Matching uses Go's RE2-compatible regexp engine.

Example rule file:

# high value targets
admin
grafana
jenkins
(dev|stage|staging)
^api\.
.*internal.*

Useful patterns:

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
^admin\.
(dev|stage|staging)
.*internal.*

Takeover-only mode accepts the same regex flags:

subflare --takeover -l subs.txt --match-regex '^admin\.' --exclude-regex '.*internal.*'

For automation workflows, tools/regex-filter-helper.js can convert one or more rule files into JSONL metadata that can later be tagged with categories or severity:

node tools/regex-filter-helper.js regex-rules.jsonl examples/regex/include-high-value.txt examples/regex/exclude-noise.txt

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JSONL Output

When --jsonl is used, each line contains one validated record with fields such as:

• host, domain
• sources, source_count, duplicates_merged
• confidence, first_seen
• a (A records), cname
• infra_asn, infra_org, infra_cdn
• takeover_confidence
• validated

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Credits & Acknowledgements

• Hidden Investigations – Cybersecurity Research & Vulnerability Disclosure.
• @sakibulalikhan – project author.
• Community recon tooling ecosystem for inspiration and benchmarking direction.

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License

This project is licensed under the Apache License 2.0. See LICENSE.

📬 Contact: hi@hiddeninvestigations.net