fix(api,frontend): isolate active share files and allowlist link schemes

backend/src/api/routers/files.py

@@ -9,6 +9,7 @@ from fastapi.responses import FileResponse, PlainTextResponse
 from utils.files import (
     content_disposition,
     counts_as_download,
+    is_active_mime,
     is_inline_mime,
     resolve_mime,
 )
@@ -20,7 +21,12 @@ router = APIRouter(tags=["files"], route_class=DishkaRoute)
 _GONE = "This link is no longer available.\n"
 _MISSING = "Not found.\n"
 
-_NO_STORE = {"Cache-Control": "private, no-store", "X-Robots-Tag": "noindex, nofollow"}
+_NO_STORE = {
+    "Cache-Control": "private, no-store",
+    "X-Robots-Tag": "noindex, nofollow",
+    "X-Content-Type-Options": "nosniff",
+}
+_SANDBOX = {"Content-Security-Policy": "sandbox"}
 
 
 def _client_ip(request: Request) -> str | None:
@@ -76,6 +82,7 @@ async def _serve(
         media_type=mime,
         headers={
             **_NO_STORE,
+            **(_SANDBOX if is_active_mime(mime) else {}),
             "Content-Disposition": content_disposition(
                 row["file_name"], attachment=attachment
             ),

backend/src/utils/files.py

@@ -67,6 +67,13 @@ _GENERIC_MIMES = {
 
 _INLINE_MIME_PREFIXES = ("image/", "video/", "audio/", "text/")
 _INLINE_MIMES = {"application/pdf", "application/json"}
+_ACTIVE_MIMES = {
+    "text/html",
+    "application/xhtml+xml",
+    "image/svg+xml",
+    "text/xml",
+    "application/xml",
+}
 
 _PREVIEW_AGENTS = (
     "telegrambot",
@@ -202,6 +209,10 @@ def is_inline_mime(mime: str | None) -> bool:
     return mime in _INLINE_MIMES or mime.startswith(_INLINE_MIME_PREFIXES)
 
 
+def is_active_mime(mime: str | None) -> bool:
+    return bool(mime) and mime.split(";", 1)[0].strip().lower() in _ACTIVE_MIMES
+
+
 def content_disposition(file_name: str, *, attachment: bool) -> str:
     kind = "attachment" if attachment else "inline"
     ascii_name = file_name.encode("ascii", "replace").decode("ascii").replace('"', "_")