fix(web): origin guard accepts an https page behind a TLS proxy; log only the site

- A portless Host now matches the default port of either the browser's
  scheme or Flask's, so nginx terminating TLS in front of a plain-http
  upstream (Origin https://pi.example -> 443, Flask sees http -> 80) no
  longer refuses every legitimate write. A non-default port still has to
  match exactly.
- The refusal log records only scheme://host[:port] of Origin/Referer, never
  a Referer's path or query (which can carry tokens), and repr()s the path.
- Docs: forward $http_host, not $host (nginx's $host drops the port).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -38,8 +38,10 @@ accepts both, but the store flags the old spelling as deprecated
   dashboard or userscript on another host) can no longer call the mutating
   API; call it server-side instead. Anyone posting a form body to
   `system/action` must switch to JSON. Behind a reverse proxy, forward the
-  original `Host` (`proxy_set_header Host $host;`); `X-Forwarded-Host` is
-  not trusted.
+  original `Host`, port included (`proxy_set_header Host $http_host;`;
+  nginx's `$host` drops the port); `X-Forwarded-Host` is not trusted. A
+  TLS-terminating proxy needs nothing more: a portless `Host` matches an
+  `https://` page.
 
 ### Fixes
 

docs/REST_API_REFERENCE.md

@@ -26,8 +26,8 @@ driving the Pi through a LAN user's browser. Scripts, curl, Home Assistant and
 the MQTT bridge send neither header and are unaffected. A browser page on
 another origin (a dashboard you host elsewhere, say) can no longer call the
 API; call it server-side instead. Behind a reverse proxy, pass the original
-`Host` through (nginx: `proxy_set_header Host $host;`) -- `X-Forwarded-Host`
-is not read.
+`Host` through, port included (nginx: `proxy_set_header Host $http_host;`;
+`$host` drops the port) -- `X-Forwarded-Host` is not read.
 
 ## Table of Contents
 

docs/WEB_INTERFACE_GUIDE.md

@@ -419,7 +419,8 @@ The API blueprint (`web_interface/blueprints/api_v3/`) is registered at
   (403 `CROSS_SITE_REQUEST`), so use the interface from its own address.
 - Scripts, curl, Home Assistant and the MQTT bridge send no such header and
   keep working. Behind a reverse proxy, forward the original `Host` header
-  (nginx: `proxy_set_header Host $host;`).
+  with its port (nginx: `proxy_set_header Host $http_host;` -- `$host`
+  drops the port).
 
 **Best Practices:**
 1. Run on a private network (not exposed to internet)

test/test_web_origin_guard.py

@@ -90,6 +90,57 @@ def test_the_same_host_on_another_port_is_another_site(probe):
     assert resp.status_code == 403
 
 
+def test_an_https_page_behind_a_tls_terminating_proxy_passes(probe):
+    # nginx terminates TLS and forwards a portless Host to the plain-http
+    # upstream: the browser's Origin is https (443), Flask sees http (80).
+    resp = probe.post('/change', headers={
+        'Host': 'pi.example', 'Origin': 'https://pi.example'})
+    assert resp.status_code == 200
+    resp = probe.post('/change', headers={
+        'Host': 'pi.example', 'Referer': 'https://pi.example/v3'})
+    assert resp.status_code == 200
+
+
+def test_a_portless_host_still_refuses_a_nondefault_port(probe):
+    # Only the standard port of either scheme counts as "no port".
+    for origin in ('https://pi.example:8443', 'http://pi.example:5000',
+                   'http://pi.example:443', 'https://evil.example'):
+        resp = probe.post('/change', headers={
+            'Host': 'pi.example', 'Origin': origin})
+        assert resp.status_code == 403, origin
+
+
+def test_an_explicit_host_port_must_match_exactly(probe):
+    # A Host with a port (the proxy forwards $http_host) is compared as is.
+    assert probe.post('/change', headers={
+        'Host': 'pi.example:8443',
+        'Origin': 'https://pi.example:8443'}).status_code == 200
+    assert probe.post('/change', headers={
+        'Host': 'pi.example:8443',
+        'Origin': 'https://pi.example'}).status_code == 403
+
+
+def test_a_refusal_logs_only_the_site_never_the_referer_path(probe, caplog):
+    # A Referer's path and query can carry tokens.
+    with caplog.at_level('WARNING', logger='web_interface.origin_guard'):
+        resp = probe.post('/change', headers={
+            'Referer': EVIL + '/page?token=s3cret#frag'})
+    assert resp.status_code == 403
+    logged = caplog.text
+    assert 'evil.example' in logged
+    assert 's3cret' not in logged
+    assert '/page' not in logged
+
+
+def test_a_refusal_log_cannot_be_forged_with_newlines(probe, caplog):
+    with caplog.at_level('WARNING', logger='web_interface.origin_guard'):
+        probe.post('/change%0D%0AFAKE', headers={'Origin': EVIL})
+    assert len(caplog.records) == 1
+    message = caplog.records[0].getMessage()
+    assert '\n' not in message and '\r' not in message
+    assert 'FAKE' in message  # the path was logged, escaped
+
+
 def test_no_origin_and_no_referer_passes(probe):
     # curl, Home Assistant, the MQTT bridge: not a browser.
     assert probe.post('/change').status_code == 200

web_interface/origin_guard.py

@@ -29,14 +29,18 @@ it follows whatever name or address the user typed: ``ledpi.local:5000``,
 portal's port 80 -> 5000 redirect keeps the Host the browser sent, and the
 setup page's fetches go back to that same host).
 
-The scheme is deliberately not compared, only host and port (with each side's
-default port filled in from its own scheme). A TLS-terminating reverse proxy
-that passes ``Host`` through makes the browser say ``https://pi.example`` while
-Flask sees ``http``; an attacker cannot use that gap, because to match they
-would need to serve a page from this same host and port. The app does not use
-``ProxyFix`` and so does not trust ``X-Forwarded-Host``: a proxy that rewrites
-``Host`` to the upstream address (nginx's default ``proxy_pass`` does) must
-be configured to pass the original one (``proxy_set_header Host $host;``).
+The scheme is deliberately not compared, only host and port. The claimed
+value's default port comes from its own scheme. A ``Host`` without a port
+means "the default port of whatever scheme the browser used", and that scheme
+is not always the one Flask sees: a TLS-terminating reverse proxy makes the
+browser say ``https://pi.example`` (443) while Flask sees ``http`` (80). So a
+portless ``Host`` accepts either default. An attacker cannot use that gap,
+because to match they would need to serve a page from this same host on its
+standard port. The app does not use ``ProxyFix`` and so does not trust
+``X-Forwarded-Host`` or ``X-Forwarded-Proto``: a proxy that rewrites ``Host``
+to the upstream address (nginx's default ``proxy_pass`` does) must be
+configured to pass the original one, port included
+(``proxy_set_header Host $http_host;`` -- nginx's ``$host`` drops the port).
 
 Not covered: DNS rebinding (an attacker's hostname re-pointed at the Pi is
 "same origin" to the browser), and anyone who can reach the port directly.
@@ -55,14 +59,14 @@ STATE_CHANGING_METHODS = frozenset({'POST', 'PUT', 'PATCH', 'DELETE'})
 _DEFAULT_PORTS = {'http': 80, 'https': 443}
 
 
-def _host_port(scheme: str, netloc: str):
-    """``(hostname, port)`` for a URL's authority, or None if it has none.
+def _authority(netloc: str):
+    """``(hostname, port)`` for an authority; port is None when it has none.
 
-    Lower-cases the host and fills in the scheme's default port, so
-    ``http://Pi.local`` and a ``Host: pi.local:80`` header compare equal.
+    Lower-cases the host and drops a trailing dot, so ``Pi.local.`` and
+    ``pi.local`` compare equal. None if the authority is unreadable.
     """
     try:
-        parts = urlsplit(f'{scheme}://{netloc}')
+        parts = urlsplit(f'//{netloc}')
         hostname = parts.hostname
         port = parts.port
     except ValueError:
@@ -70,25 +74,63 @@ def _host_port(scheme: str, netloc: str):
         return None
     if not hostname:
         return None
-    if port is None:
-        port = _DEFAULT_PORTS.get(scheme.lower())
     return hostname.lower().rstrip('.'), port
 
 
 def _url_host_port(url: str):
-    """``(hostname, port)`` for an Origin or Referer value, or None."""
+    """``(hostname, port, default_port)`` for an Origin or Referer, or None.
+
+    ``port`` is the explicit port or, failing that, the URL scheme's default,
+    which is also returned as ``default_port``.
+    """
     try:
         parts = urlsplit(url.strip())
     except ValueError:
         return None
-    if parts.scheme.lower() not in _DEFAULT_PORTS or not parts.netloc:
+    scheme = parts.scheme.lower()
+    if scheme not in _DEFAULT_PORTS or not parts.netloc:
         return None
-    return _host_port(parts.scheme.lower(), parts.netloc.rsplit('@', 1)[-1])
+    authority = _authority(parts.netloc.rsplit('@', 1)[-1])
+    if authority is None:
+        return None
+    hostname, port = authority
+    default_port = _DEFAULT_PORTS[scheme]
+    return hostname, default_port if port is None else port, default_port
 
 
-def _request_host_port():
-    """``(hostname, port)`` this request was addressed to, per its Host."""
-    return _host_port(request.scheme, request.host)
+def _names_this_server(claimed) -> bool:
+    """Whether a claimed ``(hostname, port, default_port)`` is this request's
+    own ``Host``."""
+    own = _authority(request.host)
+    if own is None:
+        return False
+    hostname, port = own
+    claimed_host, claimed_port, claimed_default = claimed
+    if claimed_host != hostname:
+        return False
+    if port is not None:
+        return claimed_port == port
+    # A portless Host is the default port of the scheme the browser used.
+    # Behind a TLS-terminating proxy that is https/443 while Flask sees
+    # http/80, so accept the default of either scheme.
+    return claimed_port in (claimed_default,
+                            _DEFAULT_PORTS.get(request.scheme))
+
+
+def _loggable(value: str) -> str:
+    """Just the ``scheme://host[:port]`` of an Origin/Referer, for the log.
+
+    A Referer's path and query can carry tokens or other private data, and
+    only the site matters when reading a refusal.
+    """
+    try:
+        parts = urlsplit(value.strip())
+        netloc = parts.netloc.rsplit('@', 1)[-1]
+    except ValueError:
+        return '<unreadable>'
+    if not parts.scheme or not netloc:
+        return '<unreadable>'
+    return f'{parts.scheme}://{netloc}'
 
 
 def check_request_origin():
@@ -115,7 +157,7 @@ def check_request_origin():
     claimed = _url_host_port(value)
     if claimed is None:
         return f'{header} header is not a valid http(s) URL'
-    if claimed != _request_host_port():
+    if not _names_this_server(claimed):
         # The claimed value is attacker-chosen: the hook logs it, but the
         # reason (echoed in the 403 body) never repeats it.
         return header + ' names a different host than this interface'
@@ -130,10 +172,14 @@ def init_app(app: Flask) -> None:
         reason = check_request_origin()
         if reason is None:
             return None
-        logger.warning("Refused cross-site %s %s: %s (Origin=%r, Referer=%r)",
+        # Only the site each header names, never a Referer's path or query
+        # (which can carry tokens); %r keeps CR/LF from forging log lines.
+        origin = request.headers.get('Origin')
+        referer = request.headers.get('Referer')
+        logger.warning("Refused cross-site %s %r: %s (Origin=%r, Referer=%r)",
                        request.method, request.path, reason,
-                       request.headers.get('Origin'),
-                       request.headers.get('Referer'))
+                       None if origin is None else _loggable(origin),
+                       None if referer is None else _loggable(referer))
         return jsonify({
             'status': 'error',
             'error_code': 'CROSS_SITE_REQUEST',