CVE-2026-70486

Summary Any authenticated user with access to a terminal server could get script of their choosing to run in the Open WebUI origin itself. The HTML file preview rendered terminal-served files in an iframe whose sandbox always granted allow-same-origin alongside allow-scripts, and the file is served from a path on the application's own origin, so the sandbox provided no isolation at all. Script in a previewed file could read the victim's session token and take over the account. Preconditions - At least one terminal server configured by an admin (TERMINAL_SERVER_CONNECTIONS, empty by default) and reachable by the victim. Deployments with no terminal server configured are not affected. - The attacker needs a normal authenticated account with access to that terminal server, no admin rights. - No victim interaction beyond having the chat open: a display_file tool call opens the preview automatically. - TERMINAL_PROXY_HEADERS unset, which is the default. An operator who had already set a restrictive Content-Security-Policy through it was not exposed, since those headers are merged into every proxied response including the served file. - The iframeSandboxAllowSameOrigin user setting is off by default, but the affected branch ignored it entirely. Impact The previewed document runs in the application origin, so it can reach the parent window, read the session token out of localStorage and exfiltrate it, which is full account takeover of the victim. If the victim is an admin, or any user holding workspace.functions, that takeover extends to server-side code execution through Functions. Getting the malicious file written and displayed still requires a prompt-injection or a social step, which is what keeps the complexity high rather than trivial. Instances with no terminal server configured were never affected, and neither was the srcdoc preview path. Fix Fixed in 0.11.0 by 65a5fad7b (#26907). The serveUrl preview branch now gates allow-same-origin behind the same iframeSand

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