w4f

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 passive TLS / CDN / WAF / edge fingerprinting · v0.1.32

Release notes → CHANGELOG.md · Vendor signature reference → docs/vendor-signatures.md

Passive TLS / CDN / WAF / edge fingerprinting for API endpoints. For any host[:port] it walks the standard client path — DNS (A/AAAA/CNAME/PTR), one SNI TLS handshake, one GET — and matches the collected signals (response headers, cookies, certificate issuer/org, CNAME/PTR suffixes, IP netblocks) against a vendor signature table to name the edge in front of the origin.

w4f --target-file hosts.txt

HOST                    EDGE        CONF  BASIS               TLS     CERT                 HTTP  NOTES
api.example.com:443     imperva +1   62%  net+cert+hdr        1.3 h2  Imperva Inc 64d       403  mTLS  BLOCK imperva
shop.example.net:443    cloudflare   82%  net+cert+cname+hdr  1.3 h2  SSL Corporati… 73d    200  ->www.shop.example.net
origin.example.org:443  nginx         7%  hdr                 1.3 h2  Let's Encrypt 21d     200
edge.example.io:443     unknown        -  -                   1.3 h2  GlobalSign nv… 161d   200

BASIS is the column that decides whether to believe the row: net+cert is ownership evidence, a bare hdr is a string the origin can set. Each host then gets a detail block and the sweep gets a rollup — see Example output.

No attack payloads. Nothing is chain-validated the way a client trusts it — this is fingerprinting, not trusting — so self-signed and privately-pinned endpoints are fingerprinted too, and the SPKI-SHA-256 pin value is reported per certificate, which is exactly the value an app's custom pinner compares against.

An optional --verify flag sends one benign <script> query to catch silent WAFs (FortiWeb, F5 ASM) that answer normal requests with plain nginx and only reveal themselves when they block something. Off by default.

Why this exists

Knowing what edge sits in front of a host decides which interception route can work at all:

• Cloudflare / anycast — a DNAT written against one resolved IP matches zero packets, because your resolver and the device's resolver return different IPs. The route is SNI-based, not IP-based.
• Imperva edge — the host may demand a client certificate at the TLS layer (mutual TLS). A proxy that can't present one gets stream reset by client after a perfectly correct app-side pinning bypass.
• CloudFront / GFE / ELB — the origin is behind a managed edge; whether the origin itself is reachable by name tells you where the capture ceiling is.
• Silent WAFs (FortiWeb) — serve nginx headers to every passive request; only an attack-shaped query gets their block page back. Passive scanning alone would report them as a bare origin.

This tool makes that a 2-second decision instead of an hour of guessing.

Install

Requirements: Python 3.10–3.12, nothing mandatory. cryptography adds full certificate details (issuer, SAN, SPKI pin, key/sig) and dnspython adds proper CNAME/PTR resolution; without either the scanner degrades gracefully (socket fallback for DNS, cert fields omitted) and the test suite still passes.

Option 1 — pipx (recommended, isolated CLI install)

pipx install w4f
w4f --version

Option 2 — uv tool

uv tool install w4f
w4f --version

Option 3 — plain pip

Prefer a virtual environment so the w4f script lands on your PATH:

python3 -m venv .venv && source .venv/bin/activate   # Windows: .venv\Scripts\activate
pip install w4f
w4f --version

Install with the optional extras (certificate + DNS depth) in one step:

pip install "w4f[full]"

Option 4 — unreleased main, or a clone

pipx install git+https://github.com/hdyrawan/w4f.git   # or uv tool / pip

Or from a clone:

git clone https://github.com/hdyrawan/w4f.git && cd w4f
pip install .
w4f --version

Option 5 — run without installing

From a clone you can run it directly, no install step at all:

git clone https://github.com/hdyrawan/w4f.git && cd w4f
python3 -m w4f --target api.example.com

For development

git clone https://github.com/hdyrawan/w4f.git && cd w4f
python3 -m venv .venv && source .venv/bin/activate
pip install -e .            # editable: code changes apply immediately
python3 -m pytest           # run the test suite

Verify & uninstall

w4f --version        # e.g. "w4f 0.1.32 — passive TLS / CDN / WAF / edge fingerprinting"
w4f --help           # full usage
pipx uninstall w4f   # or: uv tool uninstall w4f / pip uninstall w4f

Library use

The same engine the CLI drives is exposed as a plain Python function — useful for scheduling, scripting, or building your own sweep tooling:

from w4f import fingerprint_host

r = fingerprint_host("api.example.com", verify=True)
top = r["verdict"][0]                         # ranked by confidence
print(top["vendor"], top["confidence"])       # cloudflare 82
print(top["categories"])                      # ['netblock', 'cert', 'cname', 'headers']
print(r["block"]["vendor"] if r["block"] else "no WAF block")    # needs verify=True

verdict is ranked by confidence, so verdict[0] is the best-evidenced vendor. categories (added 0.1.32) lists the signal kinds behind the score, strongest first — a verdict whose categories are only headers/cookies rests on strings the origin can set.

Returns the same per-host dict the CLI's --json output contains (host, hostport, port, resolved, tls, verdict, block, error). Accepts port, timeout, path, no_http, verify, ws_path, grpc — the CLI flag equivalents. Errors are a field, never an exception: a host that fails DNS comes back with error set and verdict == [].

Usage

# one host
w4f --target api.example.com

# several hosts, one pass
w4f --target mapi.example.com --target api.example.net --target api.example.org

# a non-443 port (API/data sockets often sit off 443)
w4f --target api.example.net:6552

# an IP literal (PTR is still resolved)
w4f --target 203.0.113.10

# scan every subdomain from a subdomain-enumeration export
w4f --target-json subdomains.json --json out.json --md out.md

# plain-text host list (one per line; # comments and blanks ignored)
w4f --target-file hosts.txt

# CSV target list (uses the host/subdomain column when present, else column 1)
w4f --target-csv targets.csv

# pipeline: subdomain enumeration straight into w4f (stdin is read when no
# explicit target source is given and stdin is not a TTY)
subfinder -d example.com -silent | w4f --csv sweep.csv

# flat CSV output for spreadsheets (primary verdict per host)
w4f --target-file hosts.txt --csv sweep.csv

# SARIF 2.1.0 for security dashboards / GitHub Code Scanning
w4f --target-file hosts.txt --sarif scan.sarif

# WebSocket upgrade probe (RFC 6455) against a path
w4f --target ws.example.com --ws /socket.io

# gRPC health-check probe (grpc.health.v1.Health/Check)
w4f --target grpc.example.com --grpc

# pace requests: --delay N seconds between per-host submissions
# (per-domain backoff: 429/503 doubles the delay up to 10s, success resets)
w4f --target-file hosts.txt --delay 0.5 --csv sweep.csv

# catch silent WAFs with the one-query active probe
w4f --target api.example.com --verify

# machine-readable + markdown sweep, quiet console
w4f --target api.example.com --quiet --json out.json --md out.md

# TLS/cert/DNS only — skip the HTTP request entirely
w4f --target api.example.com --no-http

Flags

Targets may come from --target, --target-json, --target-file, --target-csv, or — when none of those is given and stdin is not a TTY — from stdin (one host per line). All sources go through the same validation (control chars / URI schemes / overlong names dropped with a warning) and are deduplicated after validation. Targets scan in parallel; the console orders them by risk (--sort) while file outputs stay sorted by host for clean run-over-run diffs. Progress and file paths go to stderr, the report to stdout — so w4f ... > report.txt and w4f ... --quiet --json out.json | jq ... keep the machine output clean.

The banner is the Rebel figlet "w4f" (patorjk taag style, x=none full-width) with w in red and f in blue. It prints on every non-quiet run, on stderr, so stdout stays parseable.

Example output

$ w4f --target api.example.com --target shop.example.net --timeout 6

                 █████ █████     ██████
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  passive TLS / CDN / WAF / edge fingerprinting   v0.1.32

HOST                    EDGE        CONF  BASIS               TLS     CERT                 HTTP  NOTES
api.example.com:443     imperva +1   62%  net+cert+hdr        1.3 h2  Imperva Inc 64d       403  mTLS  BLOCK imperva
shop.example.net:443    cloudflare   82%  net+cert+cname+hdr  1.3 h2  SSL Corporati… 73d    200  ->www.shop.example.net
origin.example.org:443  nginx         7%  hdr                 1.3 h2  Let's Encrypt 21d     200
edge.example.io:443     unknown        -  -                   1.3 h2  GlobalSign nv… 161d   200
dead.example.io:443     -              -  -                   -       -                       -  ERR DNS did not resolve

api.example.com:443  mTLS  BLOCK imperva
  edge    imperva  62%  net+cert+hdr
          header x-iinfo: 7-1234567-1234567 NNNN CT(1 1 0) · netblock: 203.0.113.10 in 203.0.113.0/24 · cert: Imperva Inc
  stack   nginx  7%  hdr
  path    403 · TLS1.3 h2
  cert    Imperva Inc · 64d left · chain verified
  pin     spki 343d1536f3666f92…

shop.example.net:443  ->www.shop.example.net
  edge    cloudflare  82%  net+cert+cname+hdr
          header server: cloudflare · header cf-ray: 9a2b4f55b2f67d43-SIN · cname: shop.example.net.cdn.cloudflare.net · +1 more
  path    -> www.shop.example.net (1 hop) · 200 · TLS1.3 h2
  cert    SSL Corporation · 73d left · chain verified
  pin     spki 0856752f53199a67…

origin.example.org:443
  edge    nginx  7%  hdr  (headers only — spoofable)
          header server: nginx
  path    200 · TLS1.3 h2
  cert    Let's Encrypt · 21d left · chain verified
  pin     spki 9c11885c885a00ab…

edge.example.io:443
  edge    unknown — no signature matched
  leads   server: acme-edge · x-acme-pop: sin1 · x-acme-request-id
  path    200 · TLS1.3 h2
  cert    GlobalSign nv-sa · 161d left · chain verified
  pin     spki a7adf62a1443f271…

dead.example.io:443  ERR DNS did not resolve
  error   DNS did not resolve

── 5 hosts · 3.4s ──────────────────────────────────────────────────────
edges     cloudflare 1 · imperva 1 · nginx 1
unknown   1  (edge.example.io:443)
flags     mTLS 1 · BLOCK 1 · errors 1
weak      1 verdict rests on headers only (spoofable) — confirm with --verify

Default mode is the triage view: a summary table of every host, a block per host with the facts the table has no room for, then a sweep rollup.

BASIS is the column to read before trusting a verdict — it names the signal categories behind it (net netblock, cert, cname, ptr, hdr header, cookie). net+cert is ownership evidence; a bare hdr is a string the origin can set, which is why origin.example.org above is flagged headers only — spoofable. Hosts are ordered by risk (errors, block pages, mTLS, unknown, weak verdicts first) — --sort host restores alphabetical order, and file outputs are always host-sorted.

An unknown host prints a leads line with the fingerprintable headers that matched no signature — that is the raw material for the next vendor file (an unknown verdict is a tool gap, not a result).

Add -v / --verbose for the FULL per-host detail (IPs, cert chain, SPKI pin, redirect chain, response headers, complete verdict evidence):

$ w4f -v --target shop.example.net:443

shop.example.net:443
ip        104.18.1.79
cname     shop.example.net.cdn.cloudflare.net
tls       TLSv1.3  TLS_AES_256_GCM_SHA384  ALPN h2
cert      SSL Corporation  (chain verified)
  san     shop.example.net, www.shop.example.net
  valid   2026-06-05 -> 2026-12-11  (73d left)
  spki    0856752f53199a67bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
  key     RSA 2048  sha256WithRSAEncryption
http      HTTP/1.1 200 OK
  chain   https://www.shop.example.net/
  final   www.shop.example.net  (headers above are from here)
  hdr     server=cloudflare
  hdr     cf-ray=9a2b4f55b2f67d43-SIN
  hdr     cf-cache-status=DYNAMIC
verdict   cloudflare (82%, net+cert+cname+hdr): header server: cloudflare; header cf-ray: 9a2b4f55b2f67d43-SIN; cname: shop.example.net.cdn.cloudflare.net; netblock: 104.18.1.79 in 104.16.0.0/13

The chain/final rows matter more than they look: the apex is often a bare redirector and the WAF only sits on www, so they say which host the headers above actually describe.

(The hosts above are illustrative — run it against any real host to see your own output.)

Colors are enabled automatically when stdout is a TTY (piped output is plain text), and disabled with NO_COLOR. The host line is cyan, critical flags (mTLS / BLOCK / ERR) are bold bright red, redirect markers and --verify block findings yellow — and each vendor name has its own color so a glance names the edge: Cloudflare bright-yellow, Akamai blue, Fastly red, AWS family cyan, Azure family bright-blue, Tencent family bright-magenta, Google GFE magenta, F5/netscaler bright-red, FortiWeb bright-yellow, Kong bright-cyan, and plain origin stacks (nginx, Apache, IIS, Varnish, …) are dimmed so the edge vs origin distinction is instantly visible. The color map is in w4f/report.py (VENDOR_COLORS) — a new vendor gets a green default; add an entry there if it deserves its own hue.

What it reports

Reading a verdict

A host behind nginx directly gets nginx only; a host behind Imperva gets imperva from headers and cert and netblock, every matching signal listed as evidence:

imperva (62%, net+cert+hdr): header x-iinfo: 7-1234567-…; netblock: … ; cert: Imperva Inc

Every match carries a confidence (0–100) summed from weighted signal categories, each category counted once:

Because each category counts once, the percentage is not a probability and signal count is not confidence: six matching headers still score 7, while one netblock hit scores 30. That is why the category list (BASIS in the table, categories in the JSON) is the part to read — it says whether a verdict rests on evidence the origin cannot fabricate. A verdict built only from hdr/cookie is marked headers only — spoofable.

Verdicts are ranked by confidence, so verdict[0] — the vendor the table, --csv and SARIF call the edge — is the best-evidenced one. A second entry is usually the origin behind that edge (imperva in front of nginx), shown as +1 in the table and on a stack line in the block. Per-vendor weights overrides are allowed; see docs/vendor-signatures.md for the full table and the "why" behind each signal.

• A blank verdict means the edge is not in the signature table — treat it as "unknown origin, no WAF/CDN signature", not "no WAF". The block prints a leads line with the fingerprintable headers that matched nothing, which is where a new signature starts.
• A passive "direct nginx" verdict is NOT proof of a bare origin. FortiWeb and F5 ASM serve plain nginx to normal requests; run --verify before concluding the origin is exposed.
• --verify findings are reported separately (block fortiweb — ...) so the passive and active layers never blur.

Security notes

• Input validation. Targets from --target-json are validated at load: control characters, URI schemes (file:// etc.), whitespace-in-hostname, and overlong names (>253 chars) are dropped with a warning. Private / internal IPs (10.x, 192.168.x, 127.x, 169.254.x) are warned but NOT dropped — scanning internal infrastructure is a legitimate use. Only run w4f against targets you are authorised to scan.
• The reported SPKI-SHA-256 is a fingerprint, not a trust anchor. w4f reports the pin value the edge presents; it does not verify it against any expected set (this is a fingerprinting tool, not a certificate-verification tool). A reported pin implies nothing about whether the endpoint is legitimate — an attacker's certificate has a pin value too.
• Output can disclose infrastructure details. --json includes cert chains, SPKI pins, CNAME/PTR records and resolved IPs (including internal ones when you scan them). Treat the output as sensitive and do not share it inadvertently.
• The unverified TLS context is deliberate. Certificate verification is disabled (via the public ssl.create_default_context() + CERT_NONE) so that self-signed / expired / wrong-hostname certs can still be read as evidence — which is the entire point of edge fingerprinting. This means an active MITM between w4f and the target is not detected; the tool reports what it was actually presented.

AWS WAF on CloudFront is silent to passive probes — a normal GET returns 200 and only --verify sees the 403 block page. Do not write "CloudFront, no WAF" for a host without a --verify run — same trap as FortiWeb (which serves plain nginx to normal requests). See docs/vendor-signatures.md and the CHANGELOG for the version-by-version detection additions (AWS Global Accelerator, Kong, AWS WAF, Tencent EdgeOne, squarespace, ...).

Signature coverage

93 vendors across six families — each one a file under w4f/signatures/ (copy _template.py to add one; see docs/vendor-signatures.md for the contributor guide):

• CDN/edge (38): Cloudflare, Cloudflare WAF, Imperva, Akamai (incl. Kona + Bot Manager E3D=), AWS CloudFront / WAF / ELB / Global Accelerator / S3 / EC2, Fastly (+ WAF/Signal Sciences), Azure Front Door, Azure App Gateway, ArvanCloud, Tencent EdgeOne / CDN, Baidu Yunjiasu, Baidu BFE, Baidu CDN, Alibaba CDN, Wangsu, ChinaCache, Huawei Cloud CDN, Volcengine DCDN, ByteDance, 360 PanYun, Baishan, NetEase CDN, Qiniu, JD Cloud, Airee, Azion, Edgecast, MaxCDN, KeyCDN, StackPath, Zenedge, DDoS-Guard.
• WAF/protection (23): FortiWeb, F5 BIG-IP ASM, NetScaler, GTM/GSLB, Sucuri, ModSecurity, NAXSI, Wallarm, Wordfence, Zscaler, Google Cloud Armor, Radware, Reblaze, Barracuda, Huawei Cloud WAF, SafeDog, Jiasule, Wangsu WAF (wswaf), Knownsec Chuang Yu Shield, 360 WangZhanBao (WZWS), Qrator, Variti, UCloud WAF (uewaf).
• Bot management (5): DataDome, PerimeterX/HUMAN, Kasada, Shape Security, Arkose.
• API gateways / platform edges (15): Kong, Tyk, Apigee, Azure API Management, Tencent gateway (stgw/tRPC), Envoy, HAProxy, Tengine, OpenResty, Cloudflare Workers, Vercel, Google Cloud Run, AWS App Runner, SGW (Shopee/Sea), WSO2 (API Manager / Carbon gateway).
• Plain origins (6): nginx, Apache, IIS, Caddy, LiteSpeed, Varnish.
• Platforms (6): Google GFE, Wix Pepyaka, Squarespace, Azure App Service, ByteDance TLB, WordPress VIP (x-rq POP header + go-vip.net CNAME).

Plus --verify block-page signatures for FortiWeb (EN + localized ID), F5 ASM, Cloudflare, Imperva and AWS WAF ("ERROR: The request could not be satisfied"), Akamai Kona, Sucuri, Wordfence, Wallarm.

Signatures are a snapshot; a new edge version can change headers, so re-run sweeps before trusting a blank verdict for a host whose writeup is old.

JSON output

--json writes the full per-host result tree. Every host is one object; errors are a field, not an exception — a bad host never aborts the run:

[
  {
    "host": "api.example.com",
    "hostport": "api.example.com:443",
    "port": 443,
    "resolved": { "cname": ["api.example.com.cdn.cloudflare.net"], "ips": ["104.18.1.79"], "ptr": [] },
    "tls": {
      "tls_version": "TLSv1.3",
      "cipher": "TLS_AES_256_GCM_SHA384",
      "alpn": "h2",
      "mtls": false,
      "chain_verified": true,
      "cert": { "subject": "CN=api.example.com", "issuer": "O=Cloudflare, Inc.", "issuer_org": "Cloudflare, Inc.", "spki_sha256": "343d1536...", "key_type": "RSA", "key_size": 2048, "days_remaining": 118 },
      "http": { "status": "HTTP/1.1 404 Not Found", "headers": { "server": "cloudflare", "cf-ray": "a2af..." }, "set-cookie-list": [], "redirects": [], "final_host": "api.example.com" }
    },
    "verdict": [
      { "vendor": "cloudflare", "signals": 7, "confidence": 82, "categories": ["netblock", "cert", "cname", "headers"], "evidence": ["header server: cloudflare", "cname: api.example.com.cdn.cloudflare.net", ...] }
    ],
    "block": null
  }
]

verdict is ordered by confidence (best-evidenced first). categories is strongest-first and is what the console renders as BASIS.

Scripting

# the verdict for every host
w4f --target-json subdomains.json --quiet --json out.json
jq -r '.[] | "\(.hostport)\t\(.verdict[0].vendor // "unknown")"' out.json

# only hosts behind a specific edge
jq -r '.[] | select(.verdict[].vendor == "cloudflare") | .hostport' out.json

# every host whose --verify probe found a WAF block page
jq -r '.[] | select(.block) | "\(.hostport)\t\(.block.vendor)"' out.json

# fail if any host errored (exit code already does this, but jq can too)
jq -e '[.[] | select(.error)] | length == 0' out.json > /dev/null

# verdicts resting only on spoofable headers/cookies — re-check these
jq -r '.[] | select((.verdict | length) > 0 and (.verdict[0].categories | inside(["headers","cookies"])))
       | "\(.hostport)\t\(.verdict[0].vendor)"' out.json

# unknown edges: the queue for the next signature file
jq -r '.[] | select(.error == null and (.verdict | length) == 0) | .hostport' out.json

# SPKI-SHA-256 pin values for every host
jq -r '.[] | "\(.hostport)\t\(.tls.cert.spki_sha256)"' out.json

Exit codes

Testing

pip install .[dev]
python -m pytest

287 tests, offline — a local TLS server with a self-signed cert exercises the real socket path without touching the internet. Coverage: fingerprint matching against real-world cases from live sweep corpora + false-positive guards (requires-gate positives/negatives, Cloudflare-WAF low-confidence, fastly cache-node vs marketing-site, regional CloudFront netblocks); confidence-first verdict ranking; the --verify block-page matcher (FortiWeb EN/ID, F5 ASM, Cloudflare, Imperva, AWS WAF, Akamai Kona, the title-at-end-of-39KB-body trap); the modular signature loader (package discovery, nested subpackages, duplicate-name / bad-regex / missing-name / unknown-key / bad-netblock rejection, W4F_SIGNATURES env override); rate limiting; WS/gRPC probes; SARIF schema shape; CSV/JSON/MD writers; CLI/report/banner (summary-table columns and alignment under color, triage-block facts, unknown-edge leads, sweep rollup, display ordering, per-vendor verdict colors); and end-to-end probe_one against the local server.

CI (GitHub Actions) runs the suite on Python 3.10/3.11/3.12 with full extras, a no-optional-deps job proving graceful degradation, and a CLI smoke check.

Known limits

• Passive layer cannot see silent WAFs. FortiWeb and F5 ASM serve plain nginx to normal requests; only the opt-in --verify probe (one benign <script> query) makes them answer with a block page. --verify is still not a full exploit-style sweep.
• The signature table is a snapshot. New edge versions can change headers/cookies; re-run before trusting a blank verdict for an old writeup.
• --verify reads the block page title — a WAF that localizes its block page beyond the EN + ID fragments matched here would need a new signature.
• Bare IP targets resolve PTR but not CNAME (there is no CNAME for an IP).

License

MIT — see LICENSE.