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bdu:2026-07458

EUVD-2026-319195

fkie_cve-2026-45318

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.3, his advisory tracks a regression of the original Excel-preview XSS (CVE-2026-44549). The same root cause — XLSX.utils.sheet_to_html() output rendered via {@html excelHtml} without DOMPurify — was reintroduced sometime after v0.8.0 and is exploitable again This vulnerability is fixed in 0.9.3.

GHSA-hcwp-82g6-8wxc — Open WebUI has stored XSS via unsanitized Office/Excel/DOCX file preview rendering ({@html} without DOMPurify)

Affected: PyPI: open-webui

## Related advisory

This advisory tracks a regression of the original Excel-preview XSS that was publicly disclosed and patched under [GHSA-jwf8-pv5p-vhmc](https://github.com/open-webui/open-webui/security/advisories/GHSA-jwf8-pv5p-vhmc) (patched in v0.8.0). The same root cause — `XLSX.utils.sheet_to_html()` output rendered via `{@html excelHtml}` without DOMPurify — was reintroduced sometime after v0.8.0 and is exploitable again as of v0.8.12 and through the version range listed above. This advisory additionally covers the related `fileOfficeHtml` sink in `src/lib/components/chat/FileNav.svelte` (lines 458 and 1285) which was not part of the jwf8 advisory's scope.

## Summary

Open WebUI renders user-uploaded Office files (Excel, DOCX) as HTML using Svelte's `{@html}` directive **without DOMPurify sanitization**. While the codebase has DOMPurify available and uses it in 9 out of 23 `{@html}` locations (39%), three file-preview rendering paths bypass it entirely, allowing Stored XSS when a user uploads a malicious document.

This is a classic **defense propagation failure**: the sanitization primitive exists in the codebase but is not consistently applied to all rendering surfaces.

## Root Cause

**The defense primitive exists**: `DOMPurify.sanitize()` is imported and used in components like `General.svelte`, `MarkdownInlineTokens.svelte`, `Banner.svelte`, and `SVGPanZoom.svelte`.

**But 3 file-preview paths skip it**:

### Occurrence 1: FilePreview.svelte — Office…

PYSEC-2026-2731 — Open WebUI has stored XSS via unsanitized Office/Excel/DOCX file preview rendering ({@html} without DOMPurify)