Summary
This issue is setup to watch for version updates in the future and serve as a reminder.
AngleSharp 0.17.1 is flagged by NuGet audit NU1902 / GHSA-pgww-w46g-26qg / CVE-2026-54570 (medium) — a MathML <annotation-xml> mutation-XSS sanitizer bypass, patched in AngleSharp 1.5.0.
Why we can't just bump it
HtmlSanitizer (currently 9.0.967) exact-pins AngleSharp [0.17.1] and AngleSharp.Css [0.17.0] in its nuspec. AngleSharp 0.17 → 1.x is a major API rewrite, so forcing 1.5.x would break HtmlSanitizer at runtime. No released HtmlSanitizer targets AngleSharp 1.x yet.
Why we're not currently exploitable
Our only untrusted-HTML sanitization path is BookmarkNoteMarkdownService (public shared-bookmark notes). It renders Markdig with .DisableHtml() (raw HTML escaped to text before it ever reaches the sanitizer) and uses a tag allowlist that excludes MathML entirely. The CVE requires injecting a live <annotation-xml> element, which this pipeline structurally prevents.
Watch: https://github.com/mganss/HtmlSanitizer/releases and the AngleSharp dependency in its nuspec.
Summary
This issue is setup to watch for version updates in the future and serve as a reminder.
AngleSharp 0.17.1is flagged by NuGet audit NU1902 / GHSA-pgww-w46g-26qg / CVE-2026-54570 (medium) — a MathML<annotation-xml>mutation-XSS sanitizer bypass, patched in AngleSharp 1.5.0.Why we can't just bump it
HtmlSanitizer(currently 9.0.967) exact-pinsAngleSharp [0.17.1]andAngleSharp.Css [0.17.0]in its nuspec. AngleSharp 0.17 → 1.x is a major API rewrite, so forcing 1.5.x would break HtmlSanitizer at runtime. No released HtmlSanitizer targets AngleSharp 1.x yet.Why we're not currently exploitable
Our only untrusted-HTML sanitization path is
BookmarkNoteMarkdownService(public shared-bookmark notes). It renders Markdig with.DisableHtml()(raw HTML escaped to text before it ever reaches the sanitizer) and uses a tag allowlist that excludes MathML entirely. The CVE requires injecting a live<annotation-xml>element, which this pipeline structurally prevents.Watch: https://github.com/mganss/HtmlSanitizer/releases and the AngleSharp dependency in its nuspec.