Summary
Open WebUI: Same-origin XSS to account takeover via terminal port-preview iframe hardcoding allow-same-origin
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_HEADERSunset and noCONTENT_SECURITY_POLICYset, 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
iframeSandboxAllowSameOriginuser setting is off by default, but the affected branch ignored it entirely.
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).
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.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-87995 has a CVSS score of 8.7 (High). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.11.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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.
Frequently Asked Questions
- What is CVE-2026-87995? CVE-2026-87995 is a high-severity cross-site scripting (XSS) vulnerability in open-webui (pip), affecting versions >= 0.8.11, <= 0.11.0. It is fixed in 0.11.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-87995? CVE-2026-87995 has a CVSS score of 8.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of open-webui are affected by CVE-2026-87995? open-webui (pip) versions >= 0.8.11, <= 0.11.0 is affected.
- Is there a fix for CVE-2026-87995? Yes. CVE-2026-87995 is fixed in 0.11.1. Upgrade to this version or later.
- Is CVE-2026-87995 exploitable, and should I be worried? Whether CVE-2026-87995 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-87995 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-87995? Upgrade
open-webuito 0.11.1 or later.