Script execution via annotation-xml parser mismatch
Published Aug 18, 2026 · Updated Aug 18, 2026
Mutation XSS in AngleSharp before 1.5.0 allows attackers to execute script in browsers via crafted annotation-xml content. MathAnnotationXmlElement never sets NodeFlags.HtmlTip for annotation-xml elements whose encoding is text/html or application/xhtml+xml, so HtmlDomBuilder.Consume parses nested tokens as foreign content; HtmlMarkupFormatter.WriteAttributeValue also leaves less-than and greater-than characters unescaped in attribute values, enabling browser reparse to activate markup hidden from sanitizer logic. Reachability depends on an application trusting AngleSharp to sanitize or safely round-trip untrusted markup and then rendering the serialized output in a browser, where the consequence is client-side script execution in the resulting page context.
Summary
What happened
Mutation XSS in AngleSharp before 1.5.0 allows attackers to execute script in browsers via crafted annotation-xml content. MathAnnotationXmlElement never sets NodeFlags.HtmlTip for annotation-xml elements whose encoding is text/html or application/xhtml+xml, so HtmlDomBuilder.Consume parses nested tokens as foreign content; HtmlMarkupFormatter.WriteAttributeValue also leaves less-than and greater-than characters unescaped in attribute values, enabling browser reparse to activate markup hidden from sanitizer logic. Reachability depends on an application trusting AngleSharp to sanitize or safely round-trip untrusted markup and then rendering the serialized output in a browser, where the consequence is client-side script execution in the resulting page context.
The record
- CVE
- CVE-2026-54570
- Published
- Aug 18, 2026
- Updated
- Aug 18, 2026
- Vendor
- AngleSharp
- Product
- AngleSharp
- Classifications
- CWE-80, T1059.007
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 18, 2026CVE publishedPublication date reported by the CVE source.
- Aug 18, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 1.5.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA-pgww-w46g-26qg proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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