diff --git a/backend/open_webui/routers/knowledge.py b/backend/open_webui/routers/knowledge.py
index af4417844..36d20bdf5 100644
--- a/backend/open_webui/routers/knowledge.py
+++ b/backend/open_webui/routers/knowledge.py
@@ -826,7 +826,11 @@ async def remove_file_from_knowledge_by_id(
         log.debug(e)
         pass
 
-    if delete_file:
+    # Only the file owner or an admin may permanently delete the underlying
+    # file.  Collaborators with KB write access can unlink a file from the
+    # knowledge base but must not be able to destroy files they do not own,
+    # as the same file may be referenced by other KBs and chats.
+    if delete_file and (file.user_id == user.id or user.role == 'admin'):
         try:
             # Remove the file's collection from vector database
             file_collection = f'file-{form_data.file_id}'