AngleSharp: HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass (CVE-2026-54570) | HOL Guard CVE

Medium · CVSS 6.9CVE-2026-54570GHSA-PGWW-W46G-26QG

AngleSharp: HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass

Answer in brief

CVE-2026-54570 records a Medium severity (CVSS 6.9) vulnerability in AngleSharp: HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass. The current sources do not mark it as known exploited. The current feed maps AngleSharp/AngleSharp (generic), AngleSharp (nuget). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 18, 2026Updated Aug 18, 2026Source checked Sep 17, 2026First seen by HOL Jul 17, 2026Material review Aug 18, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.9
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 6.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps AngleSharp/AngleSharp (generic), AngleSharp (nuget). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
AngleSharp/AngleSharpgeneric	< 1.5.0	Not reported
AngleSharpnuget	<1.5.0	1.5.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for AngleSharp/AngleSharp, AngleSharp.
Review the reported fix. Update AngleSharp to 1.5.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jul 17, 2026

Sources and claim methodology

Upstream source description

AngleSharp is a .NET library for parsing angle bracket based hyper-texts. Prior to 1.5.0, MathAnnotationXmlElement in AngleSharp/Mathml/Dom/Internal/MathAnnotationXmlElement.cs is not treated as an HTML integration point when its encoding attribute is text/html or application/xhtml+xml, causing Consume in AngleSharp/Html/Parser/HtmlDomBuilder.cs to route tokens through foreign-content parsing instead of HTML parsing. A sanitizer can therefore observe a different DOM from the browser that reparses the serialized output. An attacker can combine this namespace differential with markup-breaking characters in an attribute value so that an element hidden from the sanitizer becomes active script-capable HTML after browser reparse, resulting in mutation cross-site scripting. This issue is fixed in version 1.5.0.

Quoted source text, attributed separately from HOL analysis.