Open WebUI rendered terminal port content inside an iframe that allowed both scripts and same‑origin content. Because the proxy served the content from the same origin as the application, an authenticated user who could host code on a shared terminal server could embed malicious scripts into a port preview. When a victim with a valid account opened that preview, the browser executed the script in the victim’s browser context, enabling the attacker to hijack the victim’s session and take over their account. The flaw is a classic same‑origin cross‑site scripting (XSS) issue, identified as CWE‑1021 and CWE‑79, that can lead directly to account takeover.

Affected versions of the open‑webui product are 0.8.11 through 0.11.1 (inclusive). The vulnerability exists in the component src/lib/components/chat/FileNav/PortPreview.svelte and is fixed in release v0.11.1. All other versions prior to 0.8.11 or newer than 0.11.1 are unaffected.

The vulnerability has a CVSS score of 8.7, indicating high severity. EPSS is not available, so the current exploit probability cannot be quantified, and the issue is not listed in the CISA KEV catalog. Successful exploitation requires an authenticated attacker with access to the terminal proxy and requires the victim to visit the port preview. Because the malicious code executes in the victim’s browser origin, an attacker can retrieve authentication tokens, manipulate the session, or perform other credential‑stealing actions. Given the high severity and the ability for the attacker to leverage an already authenticated session, the risk to affected deployments is significant, especially in environments where terminal servers are shared among many users.