A cross-site scripting vulnerability exists in Open WebUI versions 0.9.0 through 0.11.0 affecting the terminal file-preview functionality. The serveUrl iframe branch incorrectly grants both allow-same-origin and allow-scripts permissions for HTML files served from the application origin. Any authenticated user with access to a configured terminal server can exploit this to execute scripts in the Open WebUI origin context. The attack allows reading victim session tokens from localStorage, enabling full account takeover. If the victim holds admin privileges or workspace.functions access, server-side code execution is also possible. The vulnerability was fixed in version 0.11.0. A GitHub security advisory and corresponding pull request have been published alongside the fix.