[Bug]: Sanitize XHTML from ReqIF files before rendering it  #57

What type of issue is this?

• Bug report
• Feature request

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of the reqifviewer
• I have searched open and closed issues to ensure it has not already been reported

Description

XHTML from the uploaded ReqIF file is rendered with new MarkupString(...) without sanitizing (for example in AttributeValuesComponent, SpecificationDetailsPage and the tree labels). A crafted file can inject script, for example through an onerror attribute, into the page of whoever opens it.

Acceptance criteria

• All XHTML from attribute values, display names and tree labels goes through one sanitizing helper; no new MarkupString(...) on file content elsewhere.
• Allow-list based on the XHTML modules ReqIF uses (text, lists, tables, object); scripts, event-handler attributes and javascript: URLs are removed. HtmlSanitizer is already a dependency of Blazor Blueprint.
• Tests with a malicious fixture (<script>, onerror, javascript: link) prove nothing executable is rendered.

Steps to Reproduce

Load requirements-and-objects.reqifz or ProR_Traceability-Template-v1.0.reqif (reqifviewer.Tests/TestData) and look at the pages mentioned above.

System Configuration

• reqifviewer version: 6.1.0 (development, with [Refactor] Blazor Blueprint app shell and Blazor Web App hosting #56)
• Environment (Operating system, version and so on): Windows 11, Chrome
• .NET Framework version: .NET 10
• Additional information: Plan item F-01 of the viewer improvement plan. Size: M.