GHSA-jmc6-2wr8-h3wj CVE-2026-87995 PYSEC-2026-4123

Open WebUI: Same-origin XSS to account takeover via terminal port-preview iframe hardcoding allow-same-origin

High PyPI

Severity: 8.7 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.42%; Chance of exploitation in the next 30 days. Higher than 36.01% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-1021 Improper Restriction of Rendered UI Layers or Frames; CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Fix: 0.11.1; Upgrade open-webui to this version or later

Description

Summary

Any authenticated user with access to a shared terminal server could get script of their choosing to run in the Open WebUI origin itself. The in-app port preview rendered the content of a previewed port in an iframe whose sandbox always granted allow-same-origin alongside allow-scripts, and that content is served from a path on the application's own origin, so the sandbox provided no isolation at all. Script served on a previewed port 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 both the attacker and the victim. Deployments with no terminal server configured are not affected.
The attacker needs a normal authenticated account with access to that terminal connection, no admin rights, plus the ability to start a process listening on a port there.
Personal terminals a user configures for themselves are not affected. Those carry an external URL, so the previewed document is cross-origin and the sandbox held.
The victim has to open the port list and click the attacker's port.
TERMINAL_PROXY_HEADERS unset and no CONTENT_SECURITY_POLICY set, which are the defaults. An operator who had already set a restrictive Content-Security-Policy through either was not exposed, since those headers apply to the proxied response.
The iframeSandboxAllowSameOrigin user setting is off by default, but the affected branch ignored it entirely.

Impact

The previewed page 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. Serving the page costs the attacker nothing beyond the terminal access they already hold, so the only real barrier is getting the victim to open that port. Instances with no terminal server configured were never affected, and neither were personal terminals pointed at an external URL.

Fix

Fixed in 0.11.1 by 54d7a2237. The port preview now gates allow-same-origin behind a terminalPreviewAllowSameOrigin user setting that is off by default, so the preview loads at an opaque origin and cannot reach the parent context. Upgrading is sufficient and no configuration change is required. Previews of pages that need same-origin access still work if a user turns that setting on, and doing so re-enables the behaviour described here for that user.

Root cause

src/lib/components/chat/FileNav/PortPreview.svelte, the preview iframe, reached by clicking a port in the file navigator's port list.
Present from 0.8.11, the first release containing the component, through 0.11.0.

Every other iframe in the application had already been moved to an opt-in same-origin setting. The port preview kept a static sandbox string with allow-same-origin baked into it, and it was missed when the equivalent problem was fixed in the file preview for 0.11.0. Because the terminal proxy is mounted under the application's own origin and forwards the upstream response and its content type without adding a Content-Security-Policy of its own unless the operator configured one, and no global CSP is set, the sandbox was the only isolation boundary left, and it was granting precisely the permission that dissolved it.

Proof of concept

On a terminal server the victim can also reach, serve an HTML page containing a script that reads window.parent.localStorage.token and sends it to a host the attacker controls. The victim opens the file navigator, switches to the port list and clicks that port. The preview opens, the script executes at the application origin, and the token is exfiltrated.

Credits

Reported by @manus-use (researcher zx / Jace).

Affected versions

PyPI

Package	Vulnerable	Fixed in
open-webui	`>= 0.8.11, < 0.11.1`	`0.11.1`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

open-webui PyPI → `0.11.1`

pip

pip install --upgrade "open-webui>=0.11.1"

poetry

poetry add "open-webui>=0.11.1"

uv

uv add "open-webui>=0.11.1"

Severity breakdown

CVSS 3.1 8.7

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: Required
Scope: Changed
Confidentiality: High
Integrity: High
Availability: None

Weakness

CWE-1021: Improper Restriction of Rendered UI Layers or Frames

The web application does not restrict or incorrectly restricts frame objects or UI layers that belong to another application or domain.

How to prevent it

Implementation: The use of X-Frame-Options allows developers of web content to restrict the usage of their application within the form of overlays, frames, or iFrames. The developer can indicate from which domains can frame the content. The concept of X-Frame-Options is well documented, but implementation of this protection mechanism is in development to cover gaps. There is a need for allowing frames from multiple domains.
Implementation: A developer can use a "frame-breaker" script in each page that should not be framed. This is very helpful for legacy browsers that do not support X-Frame-Options security feature previously mentioned. It is also important to note that this tactic has been circumvented or bypassed. Improper usage of frames can persist in the web application through nested frames. The "frame-breaking" script does not intuitively account for multiple nested frames that can be presented to the user.
Implementation: This defense-in-depth technique can be used to prevent the improper usage of frames in web applications. It prioritizes the valid sources of data to be loaded into the application through the usage of declarative policies. Based on which implementation of Content Security Policy is in use, the developer should use the "frame-ancestors" directive or the "frame-src" directive to mitigate this weakness. Both directives allow for the placement of restrictions when it comes to allowing embedded content.
Implementation: In addition to frames or iframes as previously mentioned, the web application is expected to place restrictions on whether it is allowed to be rendered within objects, embed, or applet elements.

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

How to prevent it

Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.
Implementation, Architecture and Design: Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies. For any data that will be output to another web page, especially any data that was received from external inputs, use the appropriate encoding on all non-alphanumeric characters. Parts of the same output document may require different encodings, which will vary depending on whether the output is in the: HTML body Element attributes (such as src="XYZ") URIs JavaScript sections Cascading Style Sheets and style property etc. Note that HTML Entity Encoding is only appropriate for the HTML body. Consult the XSS Prevention Cheat Sheet [REF-724] for more details on the types of encoding and escaping that are needed.
Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.
Implementation: Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component. The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
Implementation: With Struts, write all data from form beans with the bean's filter attribute set to true.
Implementation: To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XmlHttpRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When dynamically constructing web pages, use stringent allowlists that limit the character set based on the expected value of the parameter in the request. All input should be validated and cleansed, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. It is common to see data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended. Note that proper output encoding, escaping, and quoting is the most ef
Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

References

Advisories

Packages

Timeline

Sep 9, 2026 Published
Oct 1, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-wvm9-9g5j-623f Open WebUI: Users denied by the OAuth role policy can still sign in via token exchange	Medium	Also affects open-webui
GHSA-4qg5-cxx4-g927 Open WebUI: Users denied by the OAuth domain allowlist or role policy can still sign in via token exchange	Medium	Also affects open-webui
GHSA-jqhh-cjmq-vmv6 Open WebUI: Any authenticated user can hang the server via a cyclic chat message history	Medium	Also affects open-webui
GHSA-5x7x-4c3c-qf5w Open WebUI: Server-side fetches reach blocked and internal hosts via unvalidated HTTP redirect targets	Medium	Also affects open-webui
GHSA-3cgp-3cqx-j8w2 Open WebUI: Any authenticated user can hang the server via message deletion in a cyclic chat tree	Medium	Also affects open-webui
GHSA-34r3-9m95-vq73 Open WebUI: Any authenticated user can reach the Azure platform channel via server-side web fetch	High	Also affects open-webui
GHSA-2724-6cpj-gf3v Open WebUI: Non-admin users can delete admin-owned external knowledge connections via knowledge base deletion	High	Also affects open-webui
GHSA-3pf7-q2g3-wj28 Open WebUI: Any authenticated user can inject chats into another user's folder via chat completions	Medium	Also affects open-webui

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