Security fixes: SSRF, staff role escalation, SPA-only gating, throttling, encrypted keys

Findings from the audit (50-check harness across guest/user/uploader/staff/
admin) and their fixes:

- SSRF: 'Download to Library' and the staged-upload resolve path fetched
  any http(s) URL. services.validate_remote_url now enforces the e621
  media allowlist and open_remote re-validates every redirect hop; the
  download-task create endpoint and the guest proxy use them, so internal
  addresses (127.0.0.1, LAN, metadata) are rejected with 400.
- Privilege escalation: staff could promote users to staff and demote
  other staff. Role changes across the staff boundary now require an
  admin, matching the account-deletion rules; the Users page hides what
  the backend would refuse.
- SPA-only gating: /api/storage/ and /api/duplicates/* were readable by
  any authenticated account (absolute paths, duplicate groups) while the
  SPA only shows them to uploaders. They now require CanUpload.
- Throttling (REST_FRAMEWORK, env-overridable, counted in Redis):
  anon 120/min, user 600/min, login 5/min, register 20/hour, guest e621
  proxy 60/hour. Login now goes through a throttled view.
- e621 API keys are encrypted at rest with a Fernet key derived from
  SECRET_KEY (apps/accounts/crypto.py); a data migration encrypts existing
  rows and the column widens first. Reads decrypt transparently, legacy
  plaintext still works, and a changed SECRET_KEY reads as 'not
  configured' instead of leaking. Rotating SECRET_KEY now invalidates
  stored keys as well as signed media URLs.
- Hardening: the server refuses to start with DEBUG=False while SECRET_KEY
  is still the development default.

Verified: corrected harness 50/50 (guest visibility, IDOR, signed-URL
tamper/expiry, staged-upload/similarity privacy, role matrix, SSRF),
login throttles at the 6th attempt with 429, anon polling unaffected, the
guest proxy still reaches allowlisted hosts, live e621 auth works with the
decrypted key, and DB rows hold only ciphertext.

AGENTS.md

@@ -47,3 +47,20 @@ Project constraints (do not regress):
   and the server only applies the result via POST /api/files/J-x/optimize/.
 - Do not use imgdd; perceptual hashing is imagehash server-side.
 - Chat/messaging features are out of scope.
+
+Security hardening (do not weaken):
+- e621 API keys are stored Fernet-encrypted with a key derived from
+  SECRET_KEY (apps/accounts/crypto.py); rotating SECRET_KEY invalidates them
+  (and all signed media URLs), so users must re-enter the key.
+- API throttles live in REST_FRAMEWORK (env-overridable): anon 120/min,
+  user 600/min, login 5/min, register 20/hour, e621_proxy 60/hour.
+- Only admins (superusers) may grant/revoke the staff role or delete
+  staff/admin accounts; staff manage regular/uploader accounts only.
+- Storage, duplicates, delete, temp-clear, uploads and downloads require
+  upload rights (CanUpload), not merely authentication.
+- Server-side fetching only happens for allowlisted e621 media hosts via
+  services.validate_remote_url / open_remote (every redirect hop is
+  re-validated); do not call requests.get on user-supplied URLs elsewhere.
+- A repeatable audit harness (permission matrix, IDOR, guest visibility,
+  signed URLs, SSRF, throttles) was used to verify this; formalising it as
+  a test suite is still open in the roadmap.

ROADMAP.md

@@ -170,3 +170,6 @@ Files now stage first and are resolved before entering the library.
 - Anything touching e621 endpoints follows the OpenAPI spec
   (https://e621.wiki/openapi.yaml) — see AGENTS.md for how to fetch and
   which response shapes to watch out for.
+- Security review done (Aug 2026): permissions verified per role with a
+  repeatable harness, e621 keys encrypted at rest, rate limits added and the
+  download paths host-allowlisted. See AGENTS.md for the rules to keep.

backend/.env.example

@@ -2,6 +2,14 @@ SECRET_KEY=change-me-to-a-long-random-string
 DEBUG=True
 ALLOWED_HOSTS=localhost,127.0.0.1
 
+# Rate limits (per IP for anonymous, per account when signed in). Counted in
+# the shared Redis cache; the defaults fit the shell's polling.
+# THROTTLE_ANON=120/min
+# THROTTLE_USER=600/min
+# THROTTLE_LOGIN=5/min
+# THROTTLE_REGISTER=20/hour
+# THROTTLE_E621_PROXY=60/hour
+
 # Cross-origin frontends (comma separated). Same-origin keeps working with an
 # empty list; add e.g. https://j621.example.com when the SPA is served from
 # another origin than this API.

backend/apps/accounts/crypto.py

@@ -0,0 +1,48 @@
+"""Symmetric encryption for secrets stored at rest, keyed by SECRET_KEY.
+
+Used for the per-user e621 API keys: a database dump (or backup) alone does
+not expose them. Rotating SECRET_KEY makes existing values undecryptable,
+exactly like the signed media URLs stop verifying — users then re-enter
+their e621 key.
+"""
+
+import base64
+import hashlib
+
+from cryptography.fernet import Fernet, InvalidToken
+from django.conf import settings
+
+PREFIX = "enc:"
+
+
+def _fernet() -> Fernet:
+    # Derive a stable Fernet key from the project secret.
+    digest = hashlib.sha256(
+        f"j621-secret-v1:{settings.SECRET_KEY}".encode()
+    ).digest()
+    return Fernet(base64.urlsafe_b64encode(digest))
+
+
+def encrypt_secret(value: str) -> str:
+    """Encrypt for storage; empty stays empty and already-encrypted passes through."""
+    if not value:
+        return ""
+    if value.startswith(PREFIX):
+        return value
+    return PREFIX + _fernet().encrypt(value.encode()).decode()
+
+
+def decrypt_secret(value: str) -> str:
+    """Decrypt a stored value; legacy plaintext passes through.
+
+    Returns "" when the value cannot be decrypted (e.g. SECRET_KEY changed),
+    which reads as "not configured" and asks the user for the key again.
+    """
+    if not value:
+        return ""
+    if not value.startswith(PREFIX):
+        return value
+    try:
+        return _fernet().decrypt(value[len(PREFIX) :].encode()).decode()
+    except InvalidToken:
+        return ""

backend/apps/accounts/migrations/0006_encrypt_e621_api_keys.py

@@ -0,0 +1,34 @@
+from django.db import migrations, models
+
+
+def encrypt_existing_keys(apps, schema_editor):
+    """Store existing e621 API keys encrypted (idempotent)."""
+    from apps.accounts.crypto import encrypt_secret
+
+    User = apps.get_model("accounts", "User")
+    for user in User.objects.exclude(e621_api_key="").iterator():
+        if user.e621_api_key.startswith("enc:"):
+            continue
+        user.e621_api_key = encrypt_secret(user.e621_api_key)
+        user.save(update_fields=["e621_api_key"])
+
+
+def noop(apps, schema_editor):
+    pass
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("accounts", "0005_user_preferences"),
+    ]
+
+    operations = [
+        # Ciphertext is longer than the plaintext key, so widen the column
+        # before encrypting existing rows.
+        migrations.AlterField(
+            model_name="user",
+            name="e621_api_key",
+            field=models.CharField(blank=True, default="", max_length=400),
+        ),
+        migrations.RunPython(encrypt_existing_keys, noop),
+    ]

backend/apps/accounts/models.py

@@ -23,14 +23,22 @@ class User(AbstractUser):
         related_name="+",
     )
     e621_username = models.CharField(max_length=100, blank=True, default="")
-    e621_api_key = models.CharField(max_length=100, blank=True, default="")
+    # Stored encrypted (see apps/accounts/crypto.py): never the plaintext key.
+    e621_api_key = models.CharField(max_length=400, blank=True, default="")
     e621_base_url = models.CharField(max_length=200, default="https://e621.net")
     # Per-user browse preferences (landing page, default filters, grid size).
     preferences = models.JSONField(default=dict, blank=True)
 
+    @property
+    def e621_api_key_plain(self):
+        """The decrypted e621 key ("" when it cannot be decrypted)."""
+        from .crypto import decrypt_secret
+
+        return decrypt_secret(self.e621_api_key)
+
     @property
     def e621_configured(self):
-        return bool(self.e621_username and self.e621_api_key)
+        return bool(self.e621_username and self.e621_api_key_plain)
 
     @property
     def can_upload(self):

backend/apps/accounts/urls.py

@@ -1,9 +1,9 @@
 from django.urls import path
-from rest_framework.authtoken.views import obtain_auth_token
 
 from .views import (
     AvatarView,
     E621CredentialsView,
+    LoginView,
     LogoutView,
     MeView,
     PreferencesView,
@@ -12,7 +12,7 @@ from .views import (
 
 urlpatterns = [
     path("register/", RegisterView.as_view(), name="register"),
-    path("token/", obtain_auth_token, name="login"),
+    path("token/", LoginView.as_view(), name="login"),
     path("logout/", LogoutView.as_view(), name="logout"),
     path("me/", MeView.as_view(), name="me"),
     path("avatar/", AvatarView.as_view(), name="avatar"),

backend/apps/accounts/views.py

@@ -2,14 +2,17 @@ import logging
 
 from rest_framework import mixins, status, viewsets
 from rest_framework.authtoken.models import Token
+from rest_framework.authtoken.views import ObtainAuthToken
 from rest_framework.permissions import AllowAny, IsAuthenticated
 from rest_framework.response import Response
+from rest_framework.throttling import ScopedRateThrottle
 from rest_framework.views import APIView
 from django.db.models import Count, Q
 
 from apps.core.permissions import IsAppStaff
 from apps.library.models import MediaItem
 
+from .crypto import encrypt_secret
 from .models import User
 from .serializers import (
     E621CredentialsSerializer,
@@ -23,8 +26,17 @@ from .serializers import (
 logger = logging.getLogger(__name__)
 
 
+class LoginView(ObtainAuthToken):
+    """Token login, rate limited per IP to slow down credential stuffing."""
+
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "login"
+
+
 class RegisterView(APIView):
     permission_classes = [AllowAny]
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "register"
 
     def post(self, request):
         serializer = RegisterSerializer(data=request.data)
@@ -64,7 +76,7 @@ class E621CredentialsView(APIView):
     def _payload(self, user):
         return {
             "username": user.e621_username,
-            "api_key": user.e621_api_key,
+            "api_key": user.e621_api_key_plain,
             "base_url": user.e621_base_url,
             "configured": user.e621_configured,
         }
@@ -78,7 +90,7 @@ class E621CredentialsView(APIView):
         data = serializer.validated_data
         user = request.user
         user.e621_username = data["username"].strip()
-        user.e621_api_key = data["api_key"].strip()
+        user.e621_api_key = encrypt_secret(data["api_key"].strip())
         user.e621_base_url = (
             (data.get("base_url") or "https://e621.net").strip().rstrip("/")
         )
@@ -172,13 +184,28 @@ class UserViewSet(
 
     def update(self, request, *args, **kwargs):
         user = self.get_object()
+        actor = request.user
         serializer = UserUpdateSerializer(data=request.data)
         serializer.is_valid(raise_exception=True)
         data = serializer.validated_data
 
         update_fields = []
         if "role" in data:
-            user.role = data["role"]
+            new_role = data["role"]
+            # Same rule as account deletion: only admins may move accounts
+            # across the staff boundary (granting or revoking staff).
+            if (
+                not actor.is_superuser
+                and new_role != user.role
+                and (user.is_app_staff or new_role == User.ROLE_STAFF)
+            ):
+                return Response(
+                    {
+                        "detail": "Only an admin can change staff roles.",
+                    },
+                    status=status.HTTP_403_FORBIDDEN,
+                )
+            user.role = new_role
             update_fields.append("role")
         if "avatar_j_id" in data:
             item, error = resolve_avatar_item(data.get("avatar_j_id"))

backend/apps/library/e621.py

@@ -59,7 +59,11 @@ def get(user, path, params=None, timeout=30, require_auth=True):
         response = requests.get(
             f"{base}{path}",
             params=params,
-            auth=(user.e621_username, user.e621_api_key) if configured else None,
+            auth=(
+                (user.e621_username, user.e621_api_key_plain)
+                if configured
+                else None
+            ),
             headers={"User-Agent": settings.USER_AGENT},
             timeout=timeout,
         )

backend/apps/library/services.py

@@ -255,6 +255,51 @@ class DownloadCancelled(Exception):
     """Raised when a streamed download is cancelled by the user."""
 
 
+class RemoteUrlError(ValueError):
+    """The URL is not an allowed e621 media URL."""
+
+
+def validate_remote_url(url):
+    """Only http(s) URLs on the known e621 media hosts may be fetched.
+
+    Without this the download paths are an SSRF hole: any uploader could make
+    the server fetch internal addresses (127.0.0.1, LAN services, cloud
+    metadata) and read the response back through the library.
+    """
+    from urllib.parse import urlparse
+
+    parsed = urlparse(str(url or "").strip())
+    if parsed.scheme not in {"http", "https"} or not parsed.hostname:
+        raise RemoteUrlError("Only http(s) URLs can be fetched.")
+    if parsed.hostname not in settings.E621_MEDIA_HOSTS:
+        raise RemoteUrlError("That host is not an allowed e621 media host.")
+    return url
+
+
+def open_remote(url, *, max_redirects=3, **kwargs):
+    """GET an allowlisted URL, re-validating every redirect hop.
+
+    Returns a streaming ``requests`` response. Redirects are followed
+    manually so a hop cannot jump to an internal host.
+    """
+    import requests
+    from urllib.parse import urljoin
+
+    current = url
+    for _ in range(max_redirects + 1):
+        validate_remote_url(current)
+        response = requests.get(current, allow_redirects=False, **kwargs)
+        if response.is_redirect or response.is_permanent_redirect:
+            location = response.headers.get("Location")
+            response.close()
+            if not location:
+                raise RemoteUrlError("The remote server redirected without a target.")
+            current = urljoin(current, location)
+            continue
+        return response
+    raise RemoteUrlError("Too many redirects from the remote server.")
+
+
 def download_file(
     url,
     destination,
@@ -268,10 +313,8 @@ def download_file(
     worker: without it a hung socket would keep a job "downloading" forever
     and the cancel flag could never be observed.
     """
-    import requests
-
     headers = {"User-Agent": settings.USER_AGENT}
-    with requests.get(
+    with open_remote(
         url, headers=headers, stream=True, timeout=(10, read_timeout)
     ) as response:
         response.raise_for_status()

backend/apps/library/tools.py

@@ -8,7 +8,7 @@ from django.conf import settings
 from django.core.cache import cache
 from django.db.models import Count, Q
 from rest_framework import status
-from rest_framework.permissions import AllowAny, IsAuthenticated
+from rest_framework.permissions import AllowAny
 from rest_framework.response import Response
 from rest_framework.views import APIView
 
@@ -120,7 +120,7 @@ def resolve_item(data):
 class ExactDuplicatesView(APIView):
     """Items whose content exists at more than one path."""
 
-    permission_classes = [IsAuthenticated]
+    permission_classes = [CanUpload]
 
     def get(self, request):
         items = (
@@ -143,7 +143,7 @@ class ExactDuplicatesView(APIView):
 class VisualMatchesView(APIView):
     """Items visually similar to one library item."""
 
-    permission_classes = [IsAuthenticated]
+    permission_classes = [CanUpload]
 
     def post(self, request):
         threshold = parse_threshold(request.data.get("threshold"))
@@ -185,7 +185,7 @@ class VisualGroupsView(APIView):
     a personal library. Revisit with a bucketed index if libraries grow huge.
     """
 
-    permission_classes = [IsAuthenticated]
+    permission_classes = [CanUpload]
 
     def post(self, request):
         threshold = parse_threshold(request.data.get("threshold"))
@@ -450,7 +450,7 @@ def storage_info():
 class StorageView(APIView):
     """Disk usage for the watched folder, media root and temp uploads."""
 
-    permission_classes = [IsAuthenticated]
+    permission_classes = [CanUpload]
 
     def get(self, request):
         return Response(storage_info())

backend/apps/library/views.py

@@ -15,6 +15,7 @@ from rest_framework import mixins, status, viewsets
 from rest_framework.decorators import action
 from rest_framework.permissions import AllowAny, IsAuthenticatedOrReadOnly
 from rest_framework.response import Response
+from rest_framework.throttling import ScopedRateThrottle
 from rest_framework.views import APIView
 
 from . import e621, matching, services
@@ -428,9 +429,11 @@ class DownloadTaskViewSet(
         url = str(request.data.get("url") or "").strip()
         post_id = request.data.get("post_id")
         filename = str(request.data.get("filename") or "").strip()
-        if not url.startswith(("http://", "https://")):
+        try:
+            services.validate_remote_url(url)
+        except services.RemoteUrlError as exc:
             return Response(
-                {"detail": "A valid file URL is required."},
+                {"detail": str(exc)},
                 status=status.HTTP_400_BAD_REQUEST,
             )
         trimmed = services.trim_e621_post(request.data.get("post"))
@@ -521,15 +524,15 @@ class ClientDownloadView(APIView):
     """Stream an e621 file straight to the browser (no library write)."""
 
     permission_classes = [AllowAny]
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "e621_proxy"
 
     def get(self, request):
         url = str(request.query_params.get("url") or "").strip()
         filename = str(request.query_params.get("filename") or "").strip()
-        parsed = urlparse(url)
+        try:
-        if (
+            services.validate_remote_url(url)
-            parsed.scheme not in {"http", "https"}
+        except services.RemoteUrlError:
-            or parsed.hostname not in settings.E621_MEDIA_HOSTS
-        ):
             return Response(
                 {"detail": "URL not allowed."},
                 status=status.HTTP_400_BAD_REQUEST,
@@ -538,13 +541,17 @@ class ClientDownloadView(APIView):
         import requests
 
         try:
-            upstream = requests.get(
+            upstream = services.open_remote(
                 url,
                 headers={"User-Agent": settings.USER_AGENT},
                 stream=True,
                 timeout=60,
             )
             upstream.raise_for_status()
+        except services.RemoteUrlError as exc:
+            return Response(
+                {"detail": str(exc)}, status=status.HTTP_400_BAD_REQUEST
+            )
         except requests.RequestException as exc:
             return Response(
                 {"detail": f"Could not fetch the file: {exc}"},

backend/config/settings.py

@@ -6,6 +6,7 @@ import os
 import subprocess
 from pathlib import Path
 
+from django.core.exceptions import ImproperlyConfigured
 from dotenv import load_dotenv
 
 BASE_DIR = Path(__file__).resolve().parent.parent
@@ -14,6 +15,12 @@ load_dotenv(BASE_DIR / ".env")
 
 SECRET_KEY = os.getenv("SECRET_KEY", "django-insecure-dev-only-change-me")
 DEBUG = os.getenv("DEBUG", "True").lower() == "true"
+if not DEBUG and SECRET_KEY == "django-insecure-dev-only-change-me":
+    raise ImproperlyConfigured(
+        "SECRET_KEY is still the development default. Set a long random value "
+        "in backend/.env before running with DEBUG=False — it signs the media "
+        "URLs and encrypts stored e621 keys."
+    )
 ALLOWED_HOSTS = [
     host.strip()
     for host in os.getenv("ALLOWED_HOSTS", "localhost,127.0.0.1,0.0.0.0").split(",")
@@ -234,6 +241,21 @@ REST_FRAMEWORK = {
     ],
     "DEFAULT_PAGINATION_CLASS": "config.pagination.StandardPagination",
     "PAGE_SIZE": 48,
+    # Per-IP/per-user rate limits (counted in the shared Redis cache).
+    "DEFAULT_THROTTLE_CLASSES": [
+        "rest_framework.throttling.AnonRateThrottle",
+        "rest_framework.throttling.UserRateThrottle",
+    ],
+    "DEFAULT_THROTTLE_RATES": {
+        # Generous enough for the shell polling (status every 5s, stats every 2s).
+        "anon": os.getenv("THROTTLE_ANON", "120/min"),
+        "user": os.getenv("THROTTLE_USER", "600/min"),
+        # Credential stuffing / spam guards.
+        "login": os.getenv("THROTTLE_LOGIN", "5/min"),
+        "register": os.getenv("THROTTLE_REGISTER", "20/hour"),
+        # The guest e621 download proxy streams whole files.
+        "e621_proxy": os.getenv("THROTTLE_E621_PROXY", "60/hour"),
+    },
 }
 
 DEFAULT_AUTO_FIELD = "django.db.models.BigAutoField"

backend/requirements.txt

@@ -2,6 +2,7 @@ Django>=6.0,<6.2
 djangorestframework>=3.17
 django-filter>=25.1
 django-cors-headers>=4.9
+cryptography>=46.0
 Pillow>=11.0
 python-dotenv>=1.0
 requests>=2.32

frontend/src/features/users/UsersPage.tsx

@@ -47,6 +47,18 @@ function UserRow({ profile }: { profile: AdminUser }) {
 
   // Mirrors the backend rules: nobody deletes themselves, and staff can only
   // delete accounts that are not staff/admin.
+  const targetIsStaff = Boolean(
+    profile.is_superuser || profile.is_staff || profile.role === "staff",
+  );
+  const canChangeRole = Boolean(
+    actor && (actor.is_superuser || !targetIsStaff),
+  );
+  // Staff cannot grant the staff role, so it is not even offered to them.
+  const roleOptions =
+    actor?.is_superuser || targetIsStaff
+      ? ROLE_OPTIONS
+      : ROLE_OPTIONS.filter((option) => option.value !== "staff");
+
   const canDelete = Boolean(
     actor &&
       actor.id !== profile.id &&
@@ -108,10 +120,14 @@ function UserRow({ profile }: { profile: AdminUser }) {
           onChange={(event) =>
             mutation.mutate({ role: event.target.value })
           }
-          disabled={mutation.isPending}
+          disabled={mutation.isPending || !canChangeRole}
-          title="Role"
+          title={
+            canChangeRole
+              ? "Role"
+              : "Only an admin can change staff roles"
+          }
         >
-          {ROLE_OPTIONS.map((option) => (
+          {roleOptions.map((option) => (
             <option key={option.value} value={option.value}>
               {option.label}
             </option>