Fides vulnerable to Path Traversal in Webserver API

@@ -223,6 +223,10 @@ class SSHTunnelConfigNotFoundException(Exception):
     """Exception for when Fides is configured to use an SSH tunnel without config provided."""
 
 
+class MalisciousUrlException(Exception):
+    """Fides has detected a potentially maliscious URL."""
+
+
 class AuthenticationError(HTTPException):
     """To be raised when attempting to fetch an access token using
     invalid credentials.

@@ -1,6 +1,7 @@
 """
 Contains the code that sets up the API.
 """
+import os
 import sys
 from datetime import datetime, timezone
 from logging import WARNING
@@ -11,6 +12,7 @@
 from fideslog.sdk.python.event import AnalyticsEvent
 from loguru import logger
 from starlette.background import BackgroundTask
+from urllib.parse import unquote
 from uvicorn import Config, Server
 
 import fides
@@ -20,6 +22,7 @@
     log_startup,
     run_database_startup,
 )
+from fides.api.common_exceptions import MalisciousUrlException
 from fides.api.middleware import handle_audit_log_resource
 from fides.api.schemas.analytics import Event, ExtraData
 
@@ -151,13 +154,30 @@ def read_index() -> Response:
     return get_admin_index_as_response()
 
 
+def sanitise_url_path(path: str) -> str:
+    """Returns a URL path that does not contain any ../ or //"""
+    path = unquote(path)
+    path = os.path.normpath(path)
+    for token in path.split("/"):
+        if ".." in token:
+            logger.warning(f"Potentially dangerous use of URL hierarchy in path: {path}")
+            raise MalisciousUrlException()
+    return path
+
+
 @app.get("/{catchall:path}", response_class=Response, tags=["Default"])
 def read_other_paths(request: Request) -> Response:
     """
     Return related frontend files. Adapted from https://github.com/tiangolo/fastapi/issues/130
     """
     # check first if requested file exists (for frontend assets)
     path = request.path_params["catchall"]
+    logger.debug(f"Catch all path detected: {path}")
+    try:
+        path = sanitise_url_path(path)
+    except MalisciousUrlException:
+        # if a maliscious URL is detected, route the user to the index
+        return get_admin_index_as_response()
 
     # search for matching route in package (i.e. /dataset)
     ui_file = match_route(get_ui_file_map(), path)

@@ -45,3 +45,24 @@ def test_non_existent_route_404(
             f"{V1_URL_PREFIX}/route/does/not/exist/", headers=auth_header
         )
         assert resp_4.status_code == HTTP_404_NOT_FOUND
+
+    def test_malicious_url(
+        self,
+        api_client: TestClient,
+        url,
+    ) -> None:
+        malicious_paths = [
+            "../../../../../../../../../etc/passwd",
+            "..%2f..%2f..%2f..%2f..%2f..%2f..%2f..%2f..%2fetc/passwd",
+            "%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/etc/passwd",
+            "%2e%2e%2f%2e%2e%2f%2e%2e%2f%2e%2e%2f%2e%2e%2f%2e%2e%2f%2e%2e%2f%2e%2e%2f%2e%2e%2fetc/passwd",
+            "..%c0%2f..%c0%2f..%c0%2f..%c0%2f..%c0%2f..%c0%2f..%c0%2f..%c0%2f..%c0%2f/etc/passwd",
+            ".../...//.../...//.../...//.../...//.../...//.../...//.../...//.../...//.../...//etc/passwd",
+            "...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2f...%2f...%2f%2fetc/passwd",
+            "%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//%2e%2e%2e/%2e%2e%2e//etc/passwd",
+            "%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2f%2e%2e%2e%2f%2e%2e%2e%2f%2fetc/passwd",
+        ]
+        for path in malicious_paths:
+            resp = api_client.get(f"{url}/{path}")
+            assert resp.status_code == 200
+            assert resp.text == "<h1>Privacy is a Human Right!</h1>"