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Fencer Vulns
medium 5.8

CVE-2020-26237 json

Prototype Pollution in highlight.js

published 2020-11-24 5 y ago modified 2026-07-08 4 mo ago also GHSA-vfrc-7r7c-w9mx , EUVD-2020-1472

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.3%
EPSS 1.3% chance of exploitation in 30 days, percentile 71%
public exploits
0
none known

Summary

Highlight.js is a syntax highlighter written in JavaScript. Highlight.js versions before 9.18.2 and 10.1.2 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. 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.

Patch / fix

  • npm highlight.js 9.18.2, 10.1.2
  • highlightjs highlight.js 9.18.2, 10.1.2
  • highlight.js Debian 14, Debian 13, Debian 12 9.18.1+dfsg1-3

debian advisories DEBIAN-CVE-2020-26237

  • highlight.js Ubuntu Pro 16.04 LTS 8.2+ds-4ubuntu0.1~esm1
  • highlight.js Ubuntu Pro 18.04 LTS 9.12.0+dfsg1-4ubuntu0.1~esm1
  • highlight.js Ubuntu Pro 20.04 LTS 9.12.0+dfsg1-5ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2020-26237

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-26237 updated cvss 5.8

nodejs-highlight-js: prototype pollution via a crafted HTML code block

  • Red Hat Quay v3 quay/quay-rhel8 v3.6.0-62
    fixed: vendor fix RHSA-2021:3917
  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/kibana6-rhel8 Red Hat Quay v3 quay/clair-rhel8 v3.6.0-70, quay/quay-builder-rhel8 v3.6.0-44, quay/quay-operator-rhel8 v3.6.0-43, quay/quay-operator-bundle v3.6.0-48, quay/quay-bridge-operator-rhel8 v3.6.0-40, quay/quay-bridge-operator-bundle v3.6.0-35, +3 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.33% chance of exploitation in the next 30 days, higher than 71% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:N/I:H/A:N
NVD 3.1 8.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:H
NVD 2.0 4.9 AV:N/AC:M/Au:S/C:N/I:P/A:P
GitHub 3.1 5.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
npm highlight.js
<9.18.2
>=10.0.0, <10.1.2
9.18.2
10.1.2

Affected products

  • highlightjs highlight.js

Classification

Weakness
  • CWE-471 Modification of Assumed-Immutable Data (MAID)

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.