ApostropheCMS sanitize-html: SMIL animation namespace-prefix bypass allows javascript: URI injection (XSS)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-113657: 0.31% estimated exploitation activity in the next 30 days; percentile 24.28 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary sanitize-html 2.17.7 introduced animatesUrlAttribute() to block SVG animation elements (animate, animateColor, animateMotion, animateTransform, set) when their attributeName targets a URL sink like href. However, this check is bypassed when the animation element uses a namespace prefix (e.g., svg:animate instead of animate). Root Cause The animatesUrlAttribute function (index.js, line ~832) checks svgAnimationTags.indexOf(name.toLowerCase()), where svgAnimationTags contains bare local names: ["animate", "animatecolor", "animatemotion", "animatetransform", "set"]. htmlparser2 passes namespace-prefixed tag names verbatim, so svg:animate does not match animate in the array, causing the function to return false and skip the SMIL XSS protection. Ironically, the function already handles namespace prefixes correctly for the attributeName target value (line ~843): const localName = target.slice(target.lastIndexOf(":") + 1) — but this same stripping was not applied to the tag name…

Published by the source

20 Oct 2026, 18:21 UTC

Last modified by the source

20 Oct 2026, 18:30 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-374f-7chj-9948

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-374f-7chj-9948

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-374f-7chj-9948

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# Patch Next advisory brief: CVE-2026-113657

Advisory: ApostropheCMS sanitize-html: SMIL animation namespace-prefix bypass allows javascript: URI injection (XSS)
IDs: CVE-2026-113657, GHSA-374f-7chj-9948
Record: https://patchnext.com/advisories/cve-2026-113657 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: sanitize-html 2.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm sanitize-html: affected >= 2.17.7, < 2.18.0; fixed in 2.18.0

## Suggested inspection (read-only)
- `npm ls sanitize-html --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on sanitize-html.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-374f-7chj-9948 (GitHub-reviewed advisory GHSA-374f-7chj-9948 lists affected ranges: npm sanitize-html >=2.17.7 <2.18.0)
- Verified: https://osv.dev/vulnerability/GHSA-374f-7chj-9948 (OSV record GHSA-374f-7chj-9948 lists affected ranges: npm sanitize-html >=2.17.7 <2.18.0 (fixed))

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