bugfix: relax `next` verification

AUR renders its own 404 Not Found page when a bad route
is encountered. Introducing the previous verification
caused an error in this case when setting a language
while viewing the Not Found page. So, instead of checking
through routes, just make sure that the next parameter
starts with a '/' character, which removes the possibility
of any cross attacks.

+ Removed aurweb.asgi.routes; no longer needed.
Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/asgi.py

@@ -12,8 +12,6 @@ from aurweb.auth import BasicAuthBackend
 from aurweb.db import get_engine
 from aurweb.routers import accounts, auth, errors, html, sso
 
-routes = set()
-
 # Setup the FastAPI app.
 app = FastAPI(exception_handlers=errors.exceptions)
 
@@ -47,13 +45,6 @@ async def app_startup():
     # Initialize the database engine and ORM.
     get_engine()
 
-# NOTE: Always keep this dictionary updated with all routes
-# that the application contains. We use this to check for
-# parameter value verification.
-routes = {route.path for route in app.routes}
-routes.update({route.path for route in sso.router.routes})
-routes.update({route.path for route in html.router.routes})
-
 
 @app.exception_handler(HTTPException)
 async def http_exception_handler(request, exc):

aurweb/routers/html.py

@@ -32,11 +32,9 @@ async def language(request: Request,
     parameters across the redirect.
     """
     from aurweb.db import session
-    from aurweb.asgi import routes
-    if unquote(next) not in routes:
-        return HTMLResponse(
-            b"Invalid 'next' parameter.",
-            status_code=400)
+
+    if next[0] != '/':
+        return HTMLResponse(b"Invalid 'next' parameter.", status_code=400)
 
     query_string = "?" + q if q else str()
 

test/test_routes.py

@@ -61,7 +61,7 @@ def test_language_invalid_next():
     """ Test an invalid next route at '/language'. """
     post_data = {
         "set_lang": "de",
-        "next": "/BLAHBLAHFAKE"
+        "next": "https://evil.net"
     }
     with client as req:
         response = req.post("/language", data=post_data)