CVE-2026-91127: File Viewer: DOM XSS via unsafe hyperlink schemes in the legacy DOC renderer
Summary
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.
Other sources
File Viewer is a browser-native viewer for Office, PDF, CAD, archive, and other files in private and internal web applications. Prior to @file-viewer/doc 2.3.1 and msdoc-viewer 0.2.2, the legacy DOC renderer emitted document-controlled hyperlink targets into generated HTML after character escaping but without restricting URL schemes. A crafted legacy DOC file could place javascript:, vbscript:, data:, or another unsafe scheme in a rendered link, and script could execute in the embedding application's origin when a user clicked the link. The fix blocks external document links by default, allows only HTTP(S), mail, telephone, safe relative URLs, and internal bookmarks when external links are explicitly enabled, and applies mount-boundary sanitization as defense in depth. This issue is fixed in @file-viewer/doc 2.3.1 and msdoc-viewer 0.2.2.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/msdoc-viewerto a version that resolves this vulnerability.Fixed in 0.2.2 - Upgrade
Upgrade
npm/@file-viewer/docto a version that resolves this vulnerability.Fixed in 2.3.1 - Upgrade
Upgrade
@file-viewer/docto a version that resolves this vulnerability.Fixed in 2.3.1 - Upgrade
Upgrade
msdoc-viewerto a version that resolves this vulnerability.Fixed in 0.2.2
Event History
Frequently Asked Questions
Who is exposed to this issue?
Applications using the legacy DOC renderer in @file-viewer/doc before 2.3.1 or msdoc-viewer before 0.2.2 are exposed when they render attacker-controlled or otherwise untrusted legacy DOC files in a browser.
What must an attacker do to exploit it?
An attacker must provide a crafted legacy DOC file containing a hyperlink with an unsafe URL scheme, such as javascript:, vbscript:, or data:. A user must click the rendered link for script to execute in the embedding application's origin.
Are external document links enabled by default after the fix?
No. The fix blocks external document links by default. When external links are explicitly enabled, only HTTP(S), mail, telephone, safe relative URLs, and internal bookmarks are allowed.
How can exposure be remediated?
Upgrade @file-viewer/doc to 2.3.1 or later, or msdoc-viewer to 0.2.2 or later. The fixed versions restrict permitted hyperlink schemes and add mount-boundary sanitization.