CVE-2026-54570
Received Received - Intake

MathML XSS in AngleSharp via Namespace Differential

Publication date: 2026-08-18

Last updated on: 2026-08-18

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-08-18
Last Modified
2026-08-18
Generated
2026-08-18
AI Q&A
2026-08-18
EPSS Evaluated
N/A
NVD
CVE-2026-54570
EUVD
EUVD-2026-61128

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
anglesharp anglesharp 1.5.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-80 The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.

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Executive Summary

This vulnerability involves AngleSharp, a .NET library for parsing HTML-like text. A flaw in versions before 1.5.0 causes certain elements to be processed incorrectly, leading to a mismatch between what a sanitizer sees and what a browser renders. Attackers can exploit this to inject malicious scripts via crafted attribute values.

Impact Analysis

If you use a vulnerable version of AngleSharp in an application that processes user input, attackers could exploit this to execute malicious scripts in your application. This could lead to data theft, session hijacking, or defacement of your application.

Compliance Impact

This vulnerability could lead to unauthorized script execution, potentially violating data protection requirements under GDPR or HIPAA by enabling access to sensitive user data. Non-compliance risks include legal penalties and reputational damage.

Mitigation Strategies

Update AngleSharp to version 1.5.0 or later to address the vulnerability. Review any custom sanitizer configurations to ensure they account for HTML integration points and namespace differentials.

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