VulnerabilityDeferred

CVE-2026-54570

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.

MEDIUM 6.9EPSS 0.33%

Does this matter?

Lower severity and a low EPSS score (0.33%). Track it; it rarely justifies an emergency change on its own.

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.

CVSS 3.1: 6.9 MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:N
EPSS: 0.33% probability · 26th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-80
Source: security-advisories@github.com

EPSS trend

EPSS 0.3% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.