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Medium, CVSS 6.1amended

sanitize-html allowedTags Bypass via Entity-Decoded Text in nonTextTags Elements

CVE-2026-40186GHSA-9mrh-v2v3-xpfm

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (sanitize-html 2.17.3), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
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-2026-40186: 0.25% estimated exploitation activity in the next 30 days; percentile 16.22 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Commit 49d0bb7 introduced a regression in sanitize-html that bypasses allowedTags enforcement for text inside nonTextTagsArray elements (textarea and option). Entity-encoded HTML inside these elements passes through the sanitizer as decoded, unescaped HTML, allowing injection of arbitrary tags including XSS payloads. This affects any application using sanitize-html that includes option or textarea in its allowedTags configuration. Details The vulnerable code is at packages/sanitize-html/index.js:569-573: The comment is factually incorrect. htmlparser2 10.x does decode HTML entities inside both <textarea and <option elements before passing text to the ontext callback. This can be verified: Because the code assumes the text is "already properly encoded" and skips escapeHtml(), the decoded entities (<, ) are written directly to the output as literal HTML characters. This completely bypasses the allowedTags filter — any tag can be injected inside an allowed option or textarea…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-9mrh-v2v3-xpfm

  2. Revision 1 · created ·

    Published from osv record GHSA-9mrh-v2v3-xpfm

Agent brief

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

# Patch Next advisory brief: CVE-2026-40186

Advisory: sanitize-html allowedTags Bypass via Entity-Decoded Text in nonTextTags Elements
IDs: CVE-2026-40186, GHSA-9mrh-v2v3-xpfm
Record: https://patchnext.com/advisories/cve-2026-40186 (revision 2, source checked 26 Oct 2026, 12:48 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 2.17.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm sanitize-html: affected >= 2.17.2, < 2.17.3; fixed in 2.17.3

## 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://osv.dev/vulnerability/GHSA-9mrh-v2v3-xpfm (OSV record GHSA-9mrh-v2v3-xpfm lists affected ranges: npm sanitize-html >=2.17.2 <2.17.3 (fixed))
- Verified: https://github.com/advisories/GHSA-9mrh-v2v3-xpfm (GitHub-reviewed advisory GHSA-9mrh-v2v3-xpfm lists affected ranges: npm sanitize-html >=2.17.2 <2.17.3)

Commands are suggestions: review each one before running it.

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