Open WebUI: Stored XSS via unescaped KaTeX render-error fallback in rendered messages

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-70492: 0.40% estimated exploitation activity in the next 30 days; percentile 34.60 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Any authenticated user can store a chat message whose math block makes KaTeX fail with a stack overflow instead of a parse error. When that happens the renderer falls back to inserting the original math source into the page as HTML rather than as text, so script in the message runs in the browser of whoever views it. Every surface that renders messages is affected, including shared chats and channels, and the missing control is output escaping on the error path. Preconditions Default configuration, no flags involved. The attacker needs a normal user account and a way to get the target to open the content: a shared chat link, a channel the target reads, or any other message surface. No admin rights and no non-default settings are required on either side. Impact Script executes in the viewer's browser on the Open WebUI origin, which puts the session token in localStorage within reach and therefore allows taking over the viewing account. If the viewer is an administrator, that…

Published by the source

4 Aug 2026, 20:54 UTC

Last modified by the source

4 Aug 2026, 20:54 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-pwxh-7358-jq2x

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# Patch Next advisory brief: CVE-2026-70492

Advisory: Open WebUI: Stored XSS via unescaped KaTeX render-error fallback in rendered messages
IDs: CVE-2026-70492, GHSA-pwxh-7358-jq2x
Record: https://patchnext.com/advisories/cve-2026-70492 (revision 1, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: open-webui 0.11.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI open-webui: affected >= 0.10.0, < 0.11.0; fixed in 0.11.0

## Suggested inspection (read-only)
- `python -m pip show open-webui`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on open-webui.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-pwxh-7358-jq2x (GitHub-reviewed advisory GHSA-pwxh-7358-jq2x lists affected ranges: PyPI open-webui >=0.10.0 <0.11.0)

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