1422 block imports without db folder (#1424)

* Don't allow backups to be imported if they do not have a `db` folder
* Closes #1422

CTFd/utils/exports/__init__.py

@@ -96,6 +96,14 @@ def import_ctf(backup, erase=True):
             if info.file_size > max_content_length:
                 raise zipfile.LargeZipFile
 
+    # Get list of directories in zipfile
+    member_dirs = [os.path.split(m)[0] for m in members if "/" in m]
+    if "db" not in member_dirs:
+        raise Exception(
+            'CTFd couldn\'t find the "db" folder in this backup. '
+            "The backup may be malformed or corrupted and the import process cannot continue."
+        )
+
     try:
         alembic_version = json.loads(backup.open("db/alembic_version.json").read())
         alembic_version = alembic_version["results"][0]["version_num"]