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CVE-2026-54570

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

CVSS 3.1 6.9 MEDIUMCheck source for fixed versionsKEV status unknown
Original advisory

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-54570

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-54570

Published

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

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.

Source published
18 Aug 2026 17:39:51 UTC
Source modified
18 Aug 2026 19:27:44 UTC
Saved here
23 Oct 2026 15:48:27 UTC
Source terms
CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 6.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:N

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Sources read 13 Nov 14:14 UTC · 274 of 275 readable · 273 fully read · documentation 469/469 current

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