Harden production launch defaults

.env.example

@@ -2,6 +2,7 @@ DDNS_ADMIN_PASSWORD=change-me-long-random-admin-password
 DDNS_PUBLIC_BASE_URL=https://ddns.example.net
 DDNS_HOSTNAME_SUFFIX=ddns.example.net
 DDNS_DATABASE=/data/ddns.sqlite3
+DDNS_TRUSTED_HOSTS=ddns.example.net
 DDNS_DNS_PROVIDER=cloudflare
 DDNS_DNS_ZONES=ddns.example.net
 DDNS_REQUIRE_DNS_PROVIDER=1

Dockerfile

@@ -4,6 +4,10 @@ WORKDIR /app
 COPY pyproject.toml README.md /app/
 COPY router_dyndns /app/router_dyndns
 RUN pip install --no-cache-dir .
+RUN adduser --system --group --home /app routerpulse \
+    && mkdir -p /data \
+    && chown -R routerpulse:routerpulse /app /data
+USER routerpulse
 
 EXPOSE 8080
 CMD ["router-dyndns", "serve", "--host", "0.0.0.0", "--port", "8080"]

README.md

@@ -102,6 +102,7 @@ For an internet-facing DynDNS service, run behind HTTPS and require a real DNS b
 export DDNS_PUBLIC_BASE_URL='https://ddns.example.net'
 export DDNS_HOSTNAME_SUFFIX='ddns.example.net'
 export DDNS_DATABASE='/data/ddns.sqlite3'
+export DDNS_TRUSTED_HOSTS='ddns.example.net'
 export DDNS_REQUIRE_DNS_PROVIDER=1
 export DDNS_DNS_ZONES='ddns.example.net'
 export DDNS_TRUSTED_PROXY_IPS='127.0.0.1,::1'
@@ -211,6 +212,7 @@ docker compose up -d --build
 - Keep `.env` out of git.
 - Use a long random value for `DDNS_ADMIN_PASSWORD`.
 - Use a least-privilege DNS API token or TSIG key.
+- Set `DDNS_TRUSTED_HOSTS` to the public hostnames your reverse proxy will forward, for example `ddns.example.net`.
 - Configure `DDNS_TRUSTED_PROXY_IPS` only for reverse proxies that strip user-supplied forwarding headers.
 - Keep `/docs` and `/redoc` available for API users if you want a public developer surface. Admin routes are hidden from OpenAPI and still require Basic auth.
 - Leave cleanup enabled. The app periodically removes abandoned TXT challenges and generated hostnames that were never updated by a router.
@@ -224,6 +226,7 @@ Security and cleanup defaults:
 | `DDNS_RATE_LIMIT_PER_MINUTE` | `60` | Public update/API/form requests allowed per source IP and path. |
 | `DDNS_ADMIN_RATE_LIMIT_PER_MINUTE` | `20` | Admin/operator requests allowed per source IP and path. |
 | `DDNS_MAX_REQUEST_BODY_BYTES` | `16384` | Maximum accepted request body for form/API endpoints. |
+| `DDNS_TRUSTED_HOSTS` | from `DDNS_PUBLIC_BASE_URL` | Host header allowlist. Add every public hostname that should serve the app. |
 | `DDNS_CLEANUP_CHALLENGE_HOURS` | `72` | Delete unverified DNS TXT claims after this many hours. |
 | `DDNS_CLEANUP_UNUSED_ACCOUNT_HOURS` | `168` | Delete generated hostnames that never received a router update after this many hours. |
 | `DDNS_CLEANUP_INTERVAL_SECONDS` | `3600` | Run the in-app cleanup scheduler at this interval. |

docker-compose.yml

@@ -9,7 +9,7 @@ services:
     volumes:
       - ddns-data:/data
     healthcheck:
-      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8080/healthz', timeout=2).read()"]
+      test: ["CMD", "python", "-c", "import os, urllib.parse, urllib.request; host=urllib.parse.urlparse(os.environ['DDNS_PUBLIC_BASE_URL']).hostname; req=urllib.request.Request('http://127.0.0.1:8080/healthz', headers={'Host': host}); urllib.request.urlopen(req, timeout=2).read()"]
       interval: 30s
       timeout: 5s
       retries: 3

router_dyndns/ddns.py

@@ -14,6 +14,7 @@ from typing import Annotated
 from fastapi import Depends, FastAPI, Header, HTTPException, Query, Request, Response
 from fastapi.responses import FileResponse, HTMLResponse, PlainTextResponse, RedirectResponse
 from starlette.concurrency import run_in_threadpool
+from starlette.middleware.trustedhost import TrustedHostMiddleware
 from starlette.types import ASGIApp, Message, Receive, Scope, Send
 
 from .ddns_api import create_api_router
@@ -24,6 +25,7 @@ from .ddns_security import (
     client_ip,
     credentials_from_basic_auth,
     is_rate_limited_path,
+    rate_limit_bucket,
     require_admin_csrf,
 )
 from .ddns_service import DdnsService, normalize_domain, normalize_hostname
@@ -60,6 +62,31 @@ OPENAPI_TAGS = [
 
 ASSET_DIR = Path(__file__).with_name("assets")
 
+APP_JS = """
+(() => {
+  const applyTheme = () => {
+    const theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+    document.documentElement.setAttribute("data-bs-theme", theme);
+    document.documentElement.style.colorScheme = theme;
+  };
+  applyTheme();
+  window.matchMedia("(prefers-color-scheme: dark)").addEventListener("change", applyTheme);
+})();
+
+document.addEventListener("click", async (event) => {
+  const button = event.target.closest("[data-copy]");
+  if (!button) return;
+  try {
+    await navigator.clipboard.writeText(button.dataset.copy || "");
+    const old = button.textContent;
+    button.textContent = "Copied";
+    setTimeout(() => {
+      button.textContent = old;
+    }, 1200);
+  } catch (_) {}
+});
+""".strip()
+
 
 class RequestBodyTooLargeError(Exception):
     pass
@@ -99,6 +126,7 @@ def make_app(settings: DdnsSettings | None = None) -> FastAPI:
         settings = settings.model_copy(update={"admin_password": settings.shared_secret})
     if settings.require_dns_provider and not dns_backend_configured(settings):
         raise RuntimeError("DDNS_REQUIRE_DNS_PROVIDER is set but no DNS backend is configured")
+    settings.validate_launch_ready()
 
     store = DdnsStore(settings.database_path)
     store.cleanup(settings.cleanup_challenge_hours, settings.cleanup_unused_account_hours)
@@ -127,6 +155,7 @@ def make_app(settings: DdnsSettings | None = None) -> FastAPI:
         openapi_tags=OPENAPI_TAGS,
         lifespan=lifespan,
     )
+    app.add_middleware(TrustedHostMiddleware, allowed_hosts=settings.effective_trusted_hosts)
     app.add_middleware(RequestBodyLimitMiddleware, max_body_bytes=settings.max_request_body_bytes)
     app.include_router(create_api_router(settings, store, service))
 
@@ -141,7 +170,7 @@ def make_app(settings: DdnsSettings | None = None) -> FastAPI:
 
         if is_rate_limited_path(request.url.path) or _is_admin_path(request.url.path):
             limit = settings.admin_rate_limit_per_minute if _is_admin_path(request.url.path) else settings.rate_limit_per_minute
-            key = f"{client_ip(request, settings)}:{request.url.path}"
+            key = f"{client_ip(request, settings)}:{rate_limit_bucket(request.url.path)}"
             allowed = await run_in_threadpool(store.allow_rate_limit, key, limit)
             if not allowed:
                 return PlainTextResponse("rate limit exceeded", status_code=429)
@@ -154,9 +183,7 @@ def make_app(settings: DdnsSettings | None = None) -> FastAPI:
         response.headers["X-Frame-Options"] = "DENY"
         response.headers["Referrer-Policy"] = "same-origin"
         response.headers["Permissions-Policy"] = "geolocation=(), microphone=(), camera=()"
-        response.headers["Content-Security-Policy"] = (
-            "default-src 'self'; script-src 'unsafe-inline' 'self'; style-src 'unsafe-inline' 'self' https://cdn.jsdelivr.net; form-action 'self'; frame-ancestors 'none'"
-        )
+        response.headers["Content-Security-Policy"] = _content_security_policy(request.url.path)
         if settings.public_base_url.startswith("https://"):
             response.headers["Strict-Transport-Security"] = "max-age=31536000; includeSubDomains"
         return response
@@ -441,6 +468,10 @@ def make_app(settings: DdnsSettings | None = None) -> FastAPI:
     def logo_png() -> FileResponse:
         return FileResponse(ASSET_DIR / "logo.png", media_type="image/png")
 
+    @app.get("/app.js", include_in_schema=False)
+    def app_js() -> Response:
+        return Response(APP_JS, media_type="application/javascript")
+
     @app.get("/u/{update_slug}", response_class=PlainTextResponse, response_model=None)
     def slug_update(
         update_slug: str,
@@ -518,6 +549,30 @@ def _is_secret_response(request: Request) -> bool:
     return request.method == "POST" and path in {"/magic", "/request-domain", "/verify-domain", "/accounts"}
 
 
+def _content_security_policy(path: str) -> str:
+    if path in {"/docs", "/redoc", "/openapi.json"}:
+        return (
+            "default-src 'self'; "
+            "script-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; "
+            "style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; "
+            "img-src 'self' data: https://fastapi.tiangolo.com; "
+            "font-src 'self' https://cdn.jsdelivr.net; "
+            "connect-src 'self'; "
+            "form-action 'self'; "
+            "frame-ancestors 'none'"
+        )
+    return (
+        "default-src 'self'; "
+        "script-src 'self'; "
+        "style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net; "
+        "img-src 'self' data:; "
+        "font-src 'self' https://cdn.jsdelivr.net; "
+        "connect-src 'self'; "
+        "form-action 'self'; "
+        "frame-ancestors 'none'"
+    )
+
+
 def _render_public_home(
     service: DdnsService,
     settings: DdnsSettings,
@@ -1038,17 +1093,7 @@ def _page(title: str, body: str) -> str:
         <link rel="icon" href="/favicon.ico" sizes="any">
         <link rel="icon" href="/logo.svg" type="image/svg+xml">
         <link rel="apple-touch-icon" href="/logo.png">
-        <script>
-          (() => {{
-            const applyTheme = () => {{
-              const theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
-              document.documentElement.setAttribute("data-bs-theme", theme);
-              document.documentElement.style.colorScheme = theme;
-            }};
-            applyTheme();
-            window.matchMedia("(prefers-color-scheme: dark)").addEventListener("change", applyTheme);
-          }})();
-        </script>
+        <script src="/app.js" defer></script>
         <link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-sRIl4kxILFvY47J16cr9ZwB07vP4J8+LH7qKQnuqkuIAvNWLzeN8tE5YBujZqJLB" crossorigin="anonymous">
         <style>
           :root {{
@@ -1195,18 +1240,6 @@ def _page(title: str, body: str) -> str:
             h2 {{ font-size: 25px; }}
           }}
         </style>
-        <script>
-          document.addEventListener("click", async (event) => {{
-            const button = event.target.closest("[data-copy]");
-            if (!button) return;
-            try {{
-              await navigator.clipboard.writeText(button.dataset.copy || "");
-              const old = button.textContent;
-              button.textContent = "Copied";
-              setTimeout(() => {{ button.textContent = old; }}, 1200);
-            }} catch (_) {{}}
-          }});
-        </script>
       </head>
       <body>{body}</body>
     </html>

router_dyndns/ddns_models.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import os
+import urllib.parse
 from dataclasses import dataclass
 from pathlib import Path
 
@@ -13,6 +14,7 @@ class DdnsSettings(BaseModel):
     admin_password: str = Field(default="")
     allowed_hosts: set[str] = Field(default_factory=set)
     public_base_url: str = Field(default="http://localhost:8080")
+    trusted_hosts: set[str] = Field(default_factory=set)
     hostname_suffix: str = Field(default="")
     verification_prefix: str = Field(default="_router_dyndns-ddns")
     rate_limit_per_minute: int = Field(default=60, ge=1, le=10_000)
@@ -40,6 +42,31 @@ class DdnsSettings(BaseModel):
             raise ValueError("public_base_url must start with http:// or https://")
         return value.rstrip("/")
 
+    @field_validator("trusted_hosts")
+    @classmethod
+    def validate_trusted_hosts(cls, value: set[str]) -> set[str]:
+        return {host.strip().lower() for host in value if host.strip()}
+
+    @property
+    def effective_trusted_hosts(self) -> list[str]:
+        hosts = set(self.trusted_hosts)
+        public_host = urllib.parse.urlparse(self.public_base_url).hostname
+        if public_host:
+            hosts.add(public_host.lower())
+        if not self.require_dns_provider:
+            hosts.update({"testserver", "localhost", "127.0.0.1", "::1"})
+        return sorted(hosts)
+
+    def validate_launch_ready(self) -> None:
+        if not self.require_dns_provider:
+            return
+        if len(self.admin_password) < 16:
+            raise RuntimeError("DDNS_ADMIN_PASSWORD must be at least 16 characters when DDNS_REQUIRE_DNS_PROVIDER=1")
+        if not self.hostname_suffix:
+            raise RuntimeError("DDNS_HOSTNAME_SUFFIX is required when DDNS_REQUIRE_DNS_PROVIDER=1")
+        if not self.effective_trusted_hosts:
+            raise RuntimeError("At least one trusted host is required for production")
+
     @classmethod
     def from_env(cls) -> DdnsSettings:
         allowed = {
@@ -48,6 +75,7 @@ class DdnsSettings(BaseModel):
             if item.strip()
         }
         trusted_proxy_ips = _csv_set("DDNS_TRUSTED_PROXY_IPS")
+        trusted_hosts = _csv_set("DDNS_TRUSTED_HOSTS")
         dns_zones = _csv_set("DDNS_DNS_ZONES")
         return cls(
             database_path=Path(os.getenv("DDNS_DATABASE", "ddns.sqlite3")),
@@ -55,6 +83,7 @@ class DdnsSettings(BaseModel):
             admin_password=os.getenv("DDNS_ADMIN_PASSWORD", os.getenv("DDNS_SHARED_SECRET", "")),
             allowed_hosts=allowed,
             public_base_url=os.getenv("DDNS_PUBLIC_BASE_URL", "http://localhost:8080"),
+            trusted_hosts=trusted_hosts,
             hostname_suffix=os.getenv("DDNS_HOSTNAME_SUFFIX", ""),
             verification_prefix=os.getenv("DDNS_VERIFICATION_PREFIX", "_router_dyndns-ddns"),
             rate_limit_per_minute=_env_int("DDNS_RATE_LIMIT_PER_MINUTE", 60),

router_dyndns/ddns_security.py

@@ -71,11 +71,18 @@ def is_rate_limited_path(path: str) -> bool:
         "/verify-domain",
         "/nic/update",
     }
-    return path in limited_paths or path.startswith(("/u/", "/api/v1/updates/")) or path.startswith(
-        ("/api/v1/hostnames/", "/api/v1/domains/")
+    return path in limited_paths or path.startswith(("/u/", "/m/", "/d/", "/api/v1/updates/")) or path.startswith(
+        ("/api/v1/hostnames/", "/api/v1/domains/", "/api/v1/management/")
     )
 
 
+def rate_limit_bucket(path: str) -> str:
+    for prefix in ("/u/", "/m/", "/d/", "/api/v1/updates/", "/api/v1/management/"):
+        if path.startswith(prefix):
+            return prefix.rstrip("/")
+    return path
+
+
 def _trusted_proxy(peer: str, trusted: set[str]) -> bool:
     if not trusted:
         return False

tests/test_ddns.py

@@ -212,6 +212,23 @@ def test_admin_routes_are_rate_limited(tmp_path: Path) -> None:
     assert second.status_code == 429
 
 
+def test_bearer_link_routes_share_rate_limit_bucket(tmp_path: Path) -> None:
+    app = make_app(
+        DdnsSettings(
+            database_path=tmp_path / "ddns.sqlite3",
+            admin_password="admin",
+            rate_limit_per_minute=1,
+        )
+    )
+    client = TestClient(app)
+
+    first = client.get("/m/not-a-real-token")
+    second = client.get("/m/another-token")
+
+    assert first.status_code == 404
+    assert second.status_code == 429
+
+
 def test_admin_can_rotate_links_and_password(tmp_path: Path) -> None:
     settings = DdnsSettings(
         database_path=tmp_path / "ddns.sqlite3",
@@ -385,10 +402,13 @@ def test_api_docs_include_versioned_ddns_api(tmp_path: Path) -> None:
     app = make_app(DdnsSettings(database_path=tmp_path / "ddns.sqlite3", admin_password="admin"))
     client = TestClient(app)
 
+    docs = client.get("/docs")
     redoc = client.get("/redoc")
     schema = client.get("/openapi.json").json()
 
+    assert docs.status_code == 200
     assert redoc.status_code == 200
+    assert "unsafe-inline" in docs.headers["content-security-policy"]
     assert "/api/v1/hostnames/magic" in schema["paths"]
     assert "/api/v1/updates/{update_slug}" in schema["paths"]
     assert "/admin" not in schema["paths"]
@@ -398,6 +418,35 @@ def test_api_docs_include_versioned_ddns_api(tmp_path: Path) -> None:
     assert all(tag["name"] != "admin" for tag in schema["tags"])
 
 
+def test_application_pages_use_stricter_script_csp(tmp_path: Path) -> None:
+    app = make_app(DdnsSettings(database_path=tmp_path / "ddns.sqlite3", admin_password="admin"))
+    client = TestClient(app)
+
+    response = client.get("/")
+
+    assert response.status_code == 200
+    assert '<script src="/app.js" defer></script>' in response.text
+    assert "script-src 'self'" in response.headers["content-security-policy"]
+    assert "script-src 'self' 'unsafe-inline'" not in response.headers["content-security-policy"]
+    assert client.get("/app.js").status_code == 200
+
+
+def test_trusted_host_middleware_rejects_unlisted_host(tmp_path: Path) -> None:
+    app = make_app(
+        DdnsSettings(
+            database_path=tmp_path / "ddns.sqlite3",
+            admin_password="admin",
+            public_base_url="http://ddns.example.net",
+            trusted_hosts={"ddns.example.net"},
+        )
+    )
+    client = TestClient(app)
+
+    response = client.get("/", headers={"host": "evil.example.net"})
+
+    assert response.status_code == 400
+
+
 def test_api_magic_hostname_lifecycle(tmp_path: Path) -> None:
     app = make_app(
         DdnsSettings(
@@ -639,6 +688,26 @@ def test_require_dns_provider_fails_startup_without_backend(tmp_path: Path) -> N
         raise AssertionError("expected startup failure")
 
 
+def test_launch_mode_requires_strong_admin_password(tmp_path: Path) -> None:
+    try:
+        make_app(
+            DdnsSettings(
+                database_path=tmp_path / "ddns.sqlite3",
+                admin_password="admin",
+                public_base_url="http://ddns.example.net",
+                hostname_suffix="ddns.example.net",
+                dns_provider="cloudflare",
+                cloudflare_api_token="token",
+                cloudflare_zone_id="zone",
+                require_dns_provider=True,
+            )
+        )
+    except RuntimeError as exc:
+        assert "DDNS_ADMIN_PASSWORD" in str(exc)
+    else:
+        raise AssertionError("expected startup failure")
+
+
 def test_background_cleanup_removes_abandoned_setup_flows(tmp_path: Path) -> None:
     database_path = tmp_path / "ddns.sqlite3"
     app = make_app(