CVE-2020-26237: Highlight.js is a syntax highlighter written in JavaScript

Q: How do I fix CVE-2020-26237?

highlight.js: upgrade to 9.18.2, 10.1.2; debian linux: mitigate or apply the listed mitigation; mysql enterprise monitor: upgrade to newer than 8.0.30. Exact commands for each OS are on this page.

Q: Is CVE-2020-26237 being exploited?

CVE-2020-26237 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-26237 affect?

CVE-2020-26237 affects highlight.js, debian linux, mysql enterprise monitor. Severity is medium (CVSS 5.8). 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

Q: How urgent is CVE-2020-26237?

Priority 43/100. On your watchlist

This month

MEDIUM 5.8WATCHLISTUPGRADEMITIGATEUPGRADE

CVE-2020-26237 is a medium-severity flaw (CVSS 5.8) affecting highlight.js, debian linux, mysql enterprise monitor. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 p

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.8 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	Low
User interaction	Required
EPSS exploit chance	1.3% (top 29%)
CISA exploited list	No
Weakness	CWE-471
Published	2020-11-24
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: debian · highlightjs · oracle

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-11-24 23:15 UTCPublished CVE record published
2026-06-17 03:07 UTCUpdated Record last modified

highlightjs highlight.js UPGRADE

Affected: < 9.18.2 · >= 10.1.0 and < 10.1.2

Fixed in: 9.18.2, 10.1.2

Safe to downgrade to: a release before 10.1.0

1. Check installed version

npm ls highlight.js

2. UPGRADE to 9.18.2

npm install highlight.js@">=9.18.2"

3. If no update is available yet, DOWNGRADE to a release before 10.1.0

npm view highlight.js versions npm install highlight.js@"<10.1.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

debian debian linux MITIGATE

Affected: 9.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

oracle mysql enterprise monitor UPGRADE

Affected: <= 8.0.30

Fixed in: newer than 8.0.30

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mysql-enterprise-monitor || rpm -q mysql-enterprise-monitor || mysql-enterprise-monitor --version

2. UPGRADE to newer than 8.0.30 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mysql-enterprise-monitor

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mysql-enterprise-monitor

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-26237?

highlight.js: upgrade to 9.18.2, 10.1.2; debian linux: mitigate or apply the listed mitigation; mysql enterprise monitor: upgrade to newer than 8.0.30. Exact commands for each OS are on this page.

Is CVE-2020-26237 being exploited?

CVE-2020-26237 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-26237 affect?

CVE-2020-26237 affects highlight.js, debian linux, mysql enterprise monitor. Severity is medium (CVSS 5.8). 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

How urgent is CVE-2020-26237?

Priority 43/100. On your watchlist

Software pages

MySQL vulnerabilities · Debian vulnerabilities

References

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