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Critical, CVSS 10.0amended

Unsafe defaults in remark-html

CVE-2021-39199GHSA-9q5w-79cv-947m

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (remark-html 14.0.1, 13.0.2), 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

  • npm remark-html

    Affected
    < 13.0.2>= 14.0.0, <= 14.0.0
    Fixed in
    13.0.2, 14.0.1

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
10.0 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
EPSS
  • CVE-2021-39199: 1.07% estimated exploitation activity in the next 30 days; percentile 65.01 (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.

Impact The documentation of remark-html has mentioned that it was safe by default. In practise the default was never safe and had to be opted into. This means arbitrary HTML can be passed through leading to potential XSS attacks. Patches The problem has been patched in 13.0.2 and 14.0.1: remark-html is now safe by default, and the implementation matches the documentation. Workarounds On older affected versions, pass sanitize: true, like so: References n/a For more information If you have any questions or comments about this advisory: Open an issue in remark-html Email us at security@unifiedjs.com

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

    Amended from ghsa record GHSA-9q5w-79cv-947m

  2. Revision 1 · created ·

    Published from osv record GHSA-9q5w-79cv-947m

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-2021-39199

Advisory: Unsafe defaults in `remark-html`
IDs: CVE-2021-39199, GHSA-9q5w-79cv-947m
Record: https://patchnext.com/advisories/cve-2021-39199 (revision 2, source checked 26 Oct 2026, 12:21 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 10.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: remark-html 14.0.1, 13.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm remark-html: affected < 13.0.2; >= 14.0.0, <= 14.0.0; fixed in 13.0.2, 14.0.1

## Suggested inspection (read-only)
- `npm ls remark-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 remark-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-9q5w-79cv-947m (OSV record GHSA-9q5w-79cv-947m lists affected ranges: npm remark-html >=0 =14.0.0 <14.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-9q5w-79cv-947m (GitHub-reviewed advisory GHSA-9q5w-79cv-947m lists affected ranges: npm remark-html >=0 =14.0.0 <=14.0.0)

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