CVE-2026-25543
XSS Vulnerability in HtmlSanitizer Template Tag Content
Publication date: 2026-02-04
Last updated on: 2026-02-24
Assigner: GitHub, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| htmlsanitizer_project | htmlsanitizer | to 9.0.892 (exc) |
| htmlsanitizer_project | htmlsanitizer | From 9.1.878 (inc) to 9.1.893 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-79 | The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. |
| CWE-116 | The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
This vulnerability exists in the HtmlSanitizer .NET library, which is used to clean HTML fragments and documents to prevent cross-site scripting (XSS) attacks.
Prior to versions 9.0.892 and 9.1.893-beta, if the HTML template tag is allowed, the contents inside this tag are not sanitized.
The template tag is special because it does not usually render its contents unless the shadowrootmode attribute is set to open or closed.
Because the contents inside the template tag were not sanitized, malicious scripts could be embedded and potentially executed, leading to XSS attacks.
This issue has been fixed in versions 9.0.892 and 9.1.893-beta of HtmlSanitizer.
How can this vulnerability impact me? :
This vulnerability can allow attackers to inject malicious scripts into HTML content that is assumed to be safe.
If an application uses an affected version of HtmlSanitizer and allows the template tag, attackers could exploit this to perform cross-site scripting (XSS) attacks.
Such XSS attacks can lead to unauthorized actions on behalf of users, theft of sensitive information, session hijacking, or other malicious activities.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
I don't know
What immediate steps should I take to mitigate this vulnerability?
To mitigate this vulnerability, update HtmlSanitizer to version 9.0.892 or later, or 9.1.893-beta or later, where the issue has been patched.