ApostropheCMS: Mutation-XSS / allowedTags bypass via literal solidus close

Exploitation

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

CVSS

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

EPSS

• CVE-2026-63670: 0.33% estimated exploitation activity in the next 30 days; percentile 25.84 (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 A mutation-XSS / allowedTags bypass: when textarea (or xmp) is included in allowedTags, an input containing a literal </textarea/ (a solidus right after the RCDATA end-tag name) lets non-allowed markup such as <img src=x onerror=… pass through sanitizeHtml() live and unescaped, even though img/onerror are not in the allowlist. A spec-compliant browser executes the surviving handler — XSS. This is a literal-solidus variant that bypasses the two most recent fixes in this code area (CVE-2026-40186, CVE-2026-44990), both already applied in 2.17.5. The default configuration is not affected. Details sanitize-html emits the text content of HTML raw-text elements (textarea, xmp) without escaping. Two things combine: - Parser differential: on input, htmlparser2 does NOT recognize </textarea/ (solidus after the RCDATA end-tag name) as a close tag; it emits </textarea/<img … as a single raw-text node. - Unescaped passthrough: the ontext handler (index.js ~575-583) appends textarea/xmp…

Published by the source

3 Sep 2026, 20:07 UTC

Last modified by the source

3 Sep 2026, 20:07 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-jxwj-j7wr-gfrw

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# Patch Next advisory brief: CVE-2026-63670

Advisory: ApostropheCMS: Mutation-XSS / allowedTags bypass via literal ` ` solidus close
IDs: CVE-2026-63670, GHSA-jxwj-j7wr-gfrw
Record: https://patchnext.com/advisories/cve-2026-63670 (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 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: sanitize-html 2.17.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm sanitize-html: affected <= 2.17.5; fixed in 2.17.6

## 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-jxwj-j7wr-gfrw (GitHub-reviewed advisory GHSA-jxwj-j7wr-gfrw lists affected ranges: npm sanitize-html >=0 <=2.17.5)

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