diff --git a/backend/open_webui/routers/terminals.py b/backend/open_webui/routers/terminals.py
index 441b53598c..191fb96a1f 100644
--- a/backend/open_webui/routers/terminals.py
+++ b/backend/open_webui/routers/terminals.py
@@ -49,6 +49,10 @@ def _sanitize_proxy_path(path: str) -> str | None:
     # Fail closed: still encoded after the cap means the upstream would decode further into traversal.
     if unquote(decoded) != decoded:
         return None
+    # posixpath splits on '/' only, so 'a/..\..\b' survives normpath as one component.
+    # Upstreams that treat '\' as a separator would resolve it, so reject outright.
+    if '\\' in decoded:
+        return None
     had_trailing_slash = decoded.endswith('/')
     normalized = posixpath.normpath(decoded)
     # Remove any leading slashes that would reset the base