CVE-2026-26193: Open WebUI vulnerable to Stored XSS via iFrame embeds in response messages

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to version 0.6.44, aanually modifying chat history allows setting the `embeds` property on a response message, the content of which is loaded into an iFrame with a sandbox that has `allow-scripts` and `allow-same-origin` set, ignoring the "iframe Sandbox Allow Same Origin" configuration. This enables stored XSS on the affected chat. This also triggers when the chat is in the shared format. The result is a shareable link containing the payload that can be distributed to any other users on the instance. Version 0.6.44 fixes the issue.