flyfish-dev file-viewer/doc/msdoc-viewer Legacy DOC Renderer cross site scripting

Summaryinfo

A vulnerability categorized as problematic has been discovered in flyfish-dev file-viewer, doc and msdoc-viewer. The affected element is an unknown function of the component Legacy DOC Renderer. The manipulation results in cross site scripting. This vulnerability was named CVE-2026-91127. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in flyfish-dev file-viewer, doc and msdoc-viewer (affected version unknown). It has been classified as problematic. Affected is an unknown functionality of the component Legacy DOC Renderer. The manipulation with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-79. 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. This is going to have an impact on integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-91127 since 09/14/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1059.007.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• flyfish-dev

Name

• doc
• file-viewer
• msdoc-viewer

Website

• Product: https://github.com/flyfish-dev/file-viewer/

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