CVE-2026-87995 in Open WebUI
Summary
by MITRE • 09/09/2026
Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.8.11 until 0.11.1, src/lib/components/chat/FileNav/PortPreview.svelte rendered terminal port content in an iframe sandbox containing both allow-scripts and allow-same-origin. Because the terminal proxy serves that content from the Open WebUI origin, an authenticated user with access to a shared terminal server could host script on a previewed port and take over a victim's account when the victim opened the preview. This issue is fixed in version 0.11.1.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified within Open WebUI versions ranging from 0.8.11 to 0.11.1 represents a significant security flaw rooted in improper implementation of browser sandboxing mechanisms for embedded content previews. The core issue resides in the FileNav component, specifically within the PortPreview.svelte module, which is responsible for rendering terminal port contents inside an iframe element. While the developers intended to isolate this previewed content from the main application context by applying a sandbox attribute, they inadvertently included both allow-scripts and allow-same-origin permissions in that sandbox configuration. This combination effectively neutralizes the security benefits of the sandbox because it grants the embedded content full access to execute JavaScript code while simultaneously allowing that code to interact with the origin of the parent page as if it were part of the same domain. Consequently, any script executed within this iframe inherits the privileges and context of the Open WebUI application itself rather than being restricted to a isolated environment.
From an operational perspective, this architectural weakness enables a sophisticated cross-site scripting attack vector that relies on social engineering or shared infrastructure abuse. An authenticated user who has access to a shared terminal server can exploit this flaw by hosting malicious JavaScript payloads on a specific port within their controlled environment. When another authenticated victim navigates the Open WebUI interface and chooses to preview content from that same port, the application loads the attacker's hosted page into the vulnerable iframe. Because of the overly permissive sandbox settings, the malicious script executes with full trust relative to the Open WebUI origin. This allows the attacker to bypass standard cross-origin restrictions and directly manipulate the victim's session state, potentially stealing authentication tokens, reading sensitive data displayed in the interface, or performing actions on behalf of the user without their consent.
This vulnerability is best classified under CWE-1021: Improper Restriction of Rendered UI Layers or Frames, as it involves a failure to properly restrict how content from external sources is rendered and executed within a trusted application context. Furthermore, in terms of tactical mapping according to the MITRE ATT&CK framework, this flaw facilitates Initial Access through exploitation of client-side vulnerabilities and allows for Credential Access via session hijacking techniques such as Session Cookie Theft or Browser Session Hijacking. The attack chain typically involves the attacker preparing malicious content on a server they control, luring an authenticated victim into viewing that content through the application's preview feature, and then executing arbitrary JavaScript to compromise the user's active session.
The resolution for this issue was implemented in version 0.11.1 of Open WebUI by correcting the sandbox configuration parameters applied to the iframe element used for port previews. By removing or restricting the allow-scripts and allow-same-origin permissions, the application ensures that any content loaded from external ports is strictly isolated from the main application's DOM and security context. This prevents malicious scripts from accessing cookies, local storage, or other sensitive data associated with the Open WebUI origin. Organizations running instances of Open WebUI within this affected version range must prioritize upgrading to 0.11.1 or later immediately to mitigate the risk of account takeover attacks. Additionally, administrators should review their access controls for shared terminal servers to ensure that only trusted users have write permissions to ports that might be previewed by other users, adding a layer of defense-in-depth against potential exploitation attempts.