PT-2026-6439 · Nuget · Sanitize-Html
Published
2026-02-03
·
Updated
2026-02-03
CVSS v4.0
6.3
Medium
| Vector | AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N |
Impact
If the
template tag is allowed, its contents are not sanitized. The template tag is a special tag that does not usually render its contents, unless the shadowrootmode attribute is set to open or closed.The lack of sanitization of the template tag brings up two bypasses:
- it is still possible to forcibly render the contents of a
<template>tag through mutation XSS. The DOM parsers in browsers such as Chromium have a node depth limit of 512 and tags which are beyond that depth are flattened. This in turn allows elements within<template>(which are not sanitized) to be effectively 'popped out'. An example would look like this:<div>[...]<template><script>alert('xss')</script>where[...]denotes at least another 509 opening<div>tags. - If in addition to the template tag, the
shadowrootmodeattribute is allowed throughsanitizer.AllowedAttributes.Add("shadowrootmode");, the simple payload of<div><template shadowrootmode="open"><script>alert('xss')</script>would bypass the sanitizer. This is because such usage of<template>attaches a shadow root to its parent:<div>, and its contents will be rendered.
Note that the default configuration is not affected because the
template tag is disallowed by default.Patches
The problem has been patched in versions 9.0.892 and 9.1.893-beta.
Workarounds
Disallow the
template tag. It is disallowed by default.Resources
Fix
Improper Encoding or Escaping of Output
XSS
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Related Identifiers
Affected Products
Sanitize-Html