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File Viewer: DOM XSS via unsafe hyperlink schemes in the legacy DOC renderer

High severity GitHub Reviewed Published Aug 24, 2026 in flyfish-dev/file-viewer • Updated Sep 18, 2026

Package

npm @file-viewer/doc (npm)

Affected versions

<= 2.3.0

Patched versions

2.3.1
npm msdoc-viewer (npm)
<= 0.2.1
0.2.2

Description

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.

References

@wybaby168 wybaby168 published to flyfish-dev/file-viewer Aug 24, 2026
Published to the GitHub Advisory Database Sep 18, 2026
Reviewed Sep 18, 2026
Last updated Sep 18, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(15th percentile)

Weaknesses

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

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

Improper Neutralization of Script in Attributes in a Web Page

The product does not neutralize or incorrectly neutralizes javascript: or other URIs from dangerous attributes within tags, such as onmouseover, onload, onerror, or style. Learn more on MITRE.

CVE ID

CVE-2026-91127

GHSA ID

GHSA-3753-m2x2-q623

Source code

Credits

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