ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass

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ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass

ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value attribute as one flat URL and does not recognize that attributeName selecting href or xlink:href gives the sibling values, from, to, or by attribute SVG SMIL URL semantics. In configurations that allow the animate, animateColor, animateMotion, animateTransform, or set elements, a values list can begin with a safe fragment and contain a later executable destination that survives allowedSchemesAppliedToAttributes checking. When the sanitized SVG is rendered, the browser can copy that later destination into the live link, and a victim who activates the link can execute script in the application's origin. This issue is fixed in version 2.17.7.

Source published

1 Sep 2026 20:51:10 UTC

Source modified

2 Sep 2026 16:02:13 UTC

Saved here

23 Oct 2026 15:48:27 UTC

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CVE Program Terms of Use

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CVSS 3.1 · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value at…

ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value attribute as one flat URL and does not recognize that attributeName selecting href or xlink:href gives the sibling values, from, to, or by attribute SVG SMIL URL semantics. In configurations that allow the animate, animateColor, animateMotion, animateTransform, or set elements, a values list can begin with a safe fragment and contain a later executable destination that survives allowedSchemesAppliedToAttributes checking. When the sanitized SVG is rendered, the browser can copy that later destination into the live link, and a victim who activates the link can execute script in the application's origin. This issue is fixed in version 2.17.7.

Source published

Sep 1, 2026, 8:51:10 PM (timezone not stated)

Source modified

Sep 2, 2026, 4:02:13 PM (timezone not stated)

Saved here

13 Nov 2026 18:03:02 UTC

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ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value at…

ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value attribute as one flat URL and does not recognize that attributeName selecting href or xlink:href gives the sibling values, from, to, or by attribute SVG SMIL URL semantics. In configurations that allow the animate, animateColor, animateMotion, animateTransform, or set elements, a values list can begin with a safe fragment and contain a later executable destination that survives allowedSchemesAppliedToAttributes checking. When the sanitized SVG is rendered, the browser can copy that later destination into the live link, and a victim who activates the link can execute script in the application's origin. This issue is fixed in version 2.17.7.

Source published

1 Sep 2026 21:18:48 UTC

Source modified

9 Sep 2026 21:09:13 UTC

Saved here

25 Oct 2026 16:19:16 UTC

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NIST NVD usage terms; underlying source attribution retained

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CVSS 3.1 · [email protected] · Secondary · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

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 `[email protected]` 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`: ```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`: ```sh npm install [email protected] node poc.js > poc.html ``` The 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.

Source published

1 Sep 2026 21:20:01 UTC

Source modified

10 Sep 2026 03:50:54 UTC

Saved here

24 Oct 2026 13:17:17 UTC

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GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Publisher rating · MODERATE