Skip to content
Patch Next
Sign inAdd to your agent

← Actionable
Medium, CVSS 5.8amended

Prototype Pollution in highlight.js

CVE-2020-26237GHSA-vfrc-7r7c-w9mx

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (highlight.js 10.1.2, 9.18.2), 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.

Add to your agent

Affected packages

  • npm highlight.js

    Affected
    < 9.18.2>= 10.0.0, < 10.1.2
    Fixed in
    9.18.2, 10.1.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.8 · CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:N/I:H/A:N
EPSS
  • CVE-2020-26237: 1.33% estimated exploitation activity in the next 30 days; percentile 71.06 (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 Affected versions of this package are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable. The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector. If your website or application does not render user provided data it should be unaffected. Patches Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release. Workarounds Patch your library Manually patch your library to create null objects for both languages and…

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

    Amended from ghsa record GHSA-vfrc-7r7c-w9mx

  2. Revision 1 · created ·

    Published from osv record GHSA-vfrc-7r7c-w9mx

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-2020-26237

Advisory: Prototype Pollution in highlight.js
IDs: CVE-2020-26237, GHSA-vfrc-7r7c-w9mx
Record: https://patchnext.com/advisories/cve-2020-26237 (revision 2, source checked 26 Oct 2026, 12:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: highlight.js 10.1.2, 9.18.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm highlight.js: affected < 9.18.2; >= 10.0.0, < 10.1.2; fixed in 9.18.2, 10.1.2

## Suggested inspection (read-only)
- `npm ls highlight.js --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 highlight.js.
- 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-vfrc-7r7c-w9mx (OSV record GHSA-vfrc-7r7c-w9mx lists affected ranges: npm highlight.js >=0 =10.0.0 <10.1.2 (fixed))
- Verified: https://github.com/advisories/GHSA-vfrc-7r7c-w9mx (GitHub-reviewed advisory GHSA-vfrc-7r7c-w9mx lists affected ranges: npm highlight.js >=0 =10.0.0 <10.1.2)

Commands are suggestions: review each one before running it.

Loading voting…