CVE-2026-54570 AngleSharp: HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass
Attackers can exploit a parser differential in AngleSharp to bypass sanitizers and execute malicious scripts via mutation XSS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-54570?
CVE-2026-54570 is a medium-severity cross-site scripting vulnerability in AngleSharp, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-80
Which versions are affected by CVE-2026-54570?
2 open source packages ship an affected version, including AngleSharp.
| Package | Affected | Fixed in |
|---|---|---|
AngleSharp NuGet | All versions | 1.5.0 |
AngleSharp NuGet | All versions | 1.5.0 |
How do I fix CVE-2026-54570?
Upgrade AngleSharp to 1.5.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-54570 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54570 exists.
Sources
Also known as ECHO-dcab-2378-985b, GHSA-pgww-w46g-26qg.