felhom-controller/controller/scripts/secret_in_markup_gate.py

#!/usr/bin/env python3
"""secret_in_markup_gate.py — a secret must never be rendered into a template.

WHY THIS EXISTS. Three instances of ONE pattern shipped in two days, each found by hand:

    R-249  settings_security.html  {{.RetrievalPassword}}        inside a display:none span
    R-254  app_info.html           {{.InitialCreds.Password}}    inside a `hidden` span
    R-254  deploy.html             value="{{$val}}"              in a readonly type=password input

Each was "hidden" by an instruction the browser honours when DRAWING and by nothing else, so the
plaintext sat in the response body of a page the customer merely opened. **Hiding is not containment.**
A pattern found three times is not closed by searching a fourth time; it is closed by a check.

WHAT THIS GATE DOES. It reads every template and convicts any `{{ … }}` action whose expression names
a secret (password / secret / token / credential / passphrase / apikey), unless that exact expression
is on the ALLOWLIST below with a stated reason.

⚠ WHAT IT DOES *NOT* DO, STATED PLAINLY SO NOBODY READS IT AS COMPLETE COVERAGE.

  1. It is NAME-BASED, and the hole was MEASURED rather than guessed at. It catches
     `{{.InitialCreds.Password}}`, and it also catches a launder through a local variable, because the
     ASSIGNMENT names the secret (`{{$v := .InitialCreds.Password}}` is convicted). What it cannot see
     is a secret that arrives under a NEUTRAL PAGE-DATA KEY — `data["Tagline"] = creds.Password` then
     `{{.AppInfo.Tagline}}` passes this gate cleanly. Verified both ways during the 2026-08-08 session.
     The third instance above (`value="{{$val}}"` inside an `{{if eq .Type "secret"}}` branch) is that
     shape: this gate would NOT have caught it.
  2. It reasons about TEMPLATES, not about rendered output. A handler that writes a secret into a
     neutrally-named page-data key is invisible to it.
  3. Runtime body-assertion — rendering a page with a sentinel and grepping the response — is the
     check that catches all three, and it needs each page's data to be constructible. Four pages have
     that today (settings_security, app_info, deploy, backups_restore) and each has its own test; the
     other 23 page templates do NOT. Closing that gap is R-255.

So: this is the cheap layer that would have caught two of the three, plus a per-page runtime assertion
for the pages that can afford one. Together they are not a proof; they are two nets with different
holes, and the holes are named above.
"""
import os
import re
import sys

HERE = os.path.dirname(os.path.abspath(__file__))
CTRL = os.path.dirname(HERE)
TPL = os.path.join(CTRL, "internal", "web", "templates")

SECRETY = re.compile(r"pass(word|phrase)|secret|token|credential|apikey|api_key", re.I)
ACTION = re.compile(r"\{\{-?\s*(.*?)\s*-?\}\}", re.S)

# Expressions that name a secret but are NOT one, each with the reason it is safe. An entry here is a
# claim someone made; it should be short enough to re-check by eye.
ALLOWLIST = {
    # booleans / presence flags — the whole point of the R-249 and R-254 fixes
    ".HasRetrievalPassword": "boolean: whether one exists, never the value",
    ".InitialCredsHasPassword": "boolean: whether one exists, never the value",
    ".SharePasswordSet": "boolean: whether a share password is set",
    ".PasswordError": "an error MESSAGE for a failed password change, not a password",
    ".MinPassword": "the minimum LENGTH policy number",
    # form field names and types, not values
    'eq .Type "password"': "a field TYPE discriminator",
    'eq .Type "secret"': "a field TYPE discriminator",
    'eq .Type "secret_input"': "a field TYPE discriminator",
    'if or .Required (eq .Type "password")': "a field TYPE discriminator",
    'if and (not $isDeployed) (eq .Type "secret")': "guards the PRE-DEPLOY hidden input — a form must "
                                                   "carry what it submits (README §318); see R-254 site two",
    "define \"launcher_share_password\"": "a template name",
    # the CSRF token is not a secret in this sense: it is bound to the session and useless without it,
    # and it MUST be in the form for the form to work.
    ".CSRFToken": "CSRF token — session-bound, must be in the page for any POST to work",
    ".CSRFField": "CSRF token — same",
}


def check(path):
    convictions = []
    src = open(path, encoding="utf-8").read()
    for m in ACTION.finditer(src):
        expr = m.group(1).strip()
        if not SECRETY.search(expr):
            continue
        if expr in ALLOWLIST:
            continue
        # `{{if .X}}` / `{{with .X}}` where .X is allowlisted is the same claim as `.X`
        bare = re.sub(r"^(if|with|else if)\s+", "", expr).strip()
        if bare in ALLOWLIST:
            continue
        line = src[: m.start()].count("\n") + 1
        convictions.append((line, expr))
    return convictions


def main():
    if not os.path.isdir(TPL):
        print("secret-in-markup gate INCONCLUSIVE: template dir not found: %s" % TPL)
        return 2
    files = sorted(f for f in os.listdir(TPL) if f.endswith(".html"))
    if not files:
        print("secret-in-markup gate INCONCLUSIVE: no templates found in %s" % TPL)
        return 2
    total = 0
    bad = 0
    for f in files:
        total += 1
        for line, expr in check(os.path.join(TPL, f)):
            bad += 1
            print("  %s:%d renders a secret-named expression into the markup: {{%s}}" % (f, line, expr))
    if bad:
        print()
        print("SECRET-IN-MARKUP GATE FAILED: %d expression(s) across %d template(s)." % (bad, total))
        print("A secret must not be in the response body of a page the customer merely opens —")
        print("hiding it with `hidden` / display:none / type=password stops it being DRAWN and nothing else.")
        print("Fix: carry a BOOLEAN in the page data and fetch the value with an explicit authenticated")
        print("POST that sets Cache-Control: no-store and logs the act (see R-249's and R-254's endpoints).")
        print("If the expression genuinely is not a secret, add it to ALLOWLIST with the reason.")
        return 1
    print("secret-in-markup gate OK — %d templates, no secret-named expression rendered" % total)
    print("  (NAME-BASED: blind to a secret arriving under a neutral PAGE-DATA key — see the docstring)")
    return 0


if __name__ == "__main__":
    sys.exit(main())