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

Exploitation

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

CVSS

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

EPSS

• CVE-2026-84371: 0.30% estimated exploitation activity in the next 30 days; percentile 22.59 (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 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: Install and run it, then open poc.html and click Click me: The output retains the javascript: entry, and clicking the sanitized SVG displays XSS. With input changed to <a…

Published by the source

1 Sep 2026, 21:20 UTC

Last modified by the source

1 Sep 2026, 21:21 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-g8qq-57p8-ggw5

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-84371

Advisory: ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass
IDs: CVE-2026-84371, GHSA-g8qq-57p8-ggw5
Record: https://patchnext.com/advisories/cve-2026-84371 (revision 1, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: sanitize-html 2.17.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm sanitize-html: affected >= 1.9.0, <= 2.17.6; fixed in 2.17.7

## 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-g8qq-57p8-ggw5 (GitHub-reviewed advisory GHSA-g8qq-57p8-ggw5 lists affected ranges: npm sanitize-html >=1.9.0 <=2.17.6)

Commands are suggestions: review each one before running it.