CVE-2026-54570

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

Published Aug 18, 2026 CVSS 3.1 · 6.9 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-pgww-w46g-26qg AngleSharp HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass
History
Type Values Removed Values Added
First Time appeared Anglesharp
Anglesharp anglesharp
Vendors & Products Anglesharp
Anglesharp anglesharp
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title AngleSharp: HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass
Weaknesses CWE-80
References
Metrics cvssV3_1

{'score': 6.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Aug 18, 2026, 7:27 PM
Reserved
Jun 15, 2026, 7:15 PM
Status
Deferred
Published
Aug 18, 2026, 6:18 PM
Modified
Sep 18, 2026, 8:09 PM