# CVE-2026-91127: File Viewer: DOM XSS via unsafe hyperlink schemes in the legacy DOC renderer

> CVE-2026-91127 (GitHub advisory GHSA-3753-m2x2-q623) is a high-severity vulnerability with a CVSS 3.1 base score of 8.2, classed as Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (CWE-79), in @file-viewer/doc (npm) and msdoc-viewer (npm). Fixed versions: @file-viewer/doc 2.3.1; msdoc-viewer 0.2.2.

Canonical page: https://cveminer.com/vulnerabilities/CVE-2026-91127

| Field | Value |
| --- | --- |
| CVE | CVE-2026-91127 |
| GHSA | GHSA-3753-m2x2-q623 |
| Severity | High |
| CVSS 3.1 | 8.2 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N` (GitHub Advisory Database) |
| CWE | CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'); CWE-83 Improper Neutralization of Script in Attributes in a Web Page |
| EPSS | 0.23% (higher than 14% of CVEs) |
| CISA KEV | Not listed |
| Published | 18 Sept 2026 |
| Modified | 18 Sept 2026 |

## Description

Before 2.3.1, the legacy `.doc` renderer emitted document hyperlink targets after HTML escaping but without a URL-scheme allowlist. A crafted `.doc` could therefore render a live `javascript:`, `vbscript:`, `data:`, or similarly unsafe link. Script could execute in the embedding origin if a viewer clicked it.

##### Impact

Applications rendering untrusted legacy `.doc` files with `@file-viewer/doc` or the `msdoc-viewer` compatibility package could expose their origin to attacker-controlled script after link interaction.

##### Fix

Version 2.3.1 centralizes link handling, removes control-character and scheme confusion, blocks external document links by default, and in explicit allow mode accepts only HTTP(S), mail, telephone, safe relative URLs, and internal bookmarks. The renderer output is safe before mounting, with mount-boundary sanitization as defense in depth. The `msdoc-viewer` compatibility release containing the fix is 0.2.2.

Thanks to @shashank420 for responsibly reporting this issue.

## Affected packages

| Package | Ecosystem | PURL | Vulnerable versions | Fixed in |
| --- | --- | --- | --- | --- |
| @file-viewer/doc | npm | `pkg:npm/%40file-viewer/doc` | <= 2.3.0 | 2.3.1 |
| msdoc-viewer | npm | `pkg:npm/msdoc-viewer` | <= 0.2.1 | 0.2.2 |

## Fix commits

- Patch: https://github.com/flyfish-dev/file-viewer/commit/ef045680f8d9830a3eee9612f7df46a734361b07

## Questions

**What is the GHSA ID for CVE-2026-91127?**

GitHub tracks CVE-2026-91127 as GHSA-3753-m2x2-q623.

**What is the CVSS score of CVE-2026-91127?**

CVE-2026-91127 has a CVSS 3.1 base score of 8.2 (High), vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N.

**Which versions are affected by CVE-2026-91127?**

@file-viewer/doc (npm): <= 2.3.0. msdoc-viewer (npm): <= 0.2.1.

**How do I fix CVE-2026-91127?**

Upgrade each package to its fixed version: @file-viewer/doc 2.3.1; msdoc-viewer 0.2.2. The fix is in commit ef04568.

**What is the Package URL (PURL) for CVE-2026-91127?**

The affected packages' PURLs are pkg:npm/%40file-viewer/doc and pkg:npm/msdoc-viewer.

**Is CVE-2026-91127 exploited in the wild?**

CISA's Known Exploited Vulnerabilities catalog doesn't list CVE-2026-91127. That means no confirmed exploitation has been catalogued, not that it is safe to leave unpatched. EPSS estimates a 0.23% chance of exploitation in the next 30 days, higher than 14% of CVEs.

## References

- https://github.com/flyfish-dev/file-viewer/commit/ef045680f8d9830a3eee9612f7df46a734361b07 (fix)
- https://github.com/flyfish-dev/file-viewer/security/advisories/GHSA-3753-m2x2-q623 (advisory)
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91127.json (advisory)
- https://nvd.nist.gov/vuln/detail/CVE-2026-91127 (advisory)
- https://github.com/advisories/GHSA-3753-m2x2-q623 (advisory)
- https://github.com/flyfish-dev/file-viewer (package)
- https://github.com/flyfish-dev/file-viewer/releases/tag/v2.3.1

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Source: CVEminer (https://cveminer.com/vulnerabilities/CVE-2026-91127), compiled from OSV (GitHub advisory), GitHub Advisory Database, OSV (CVE record), CVE.org, CISA KEV catalog. OSV and GitHub Advisory Database content is licensed CC BY 4.0.