CVE-2021-24591: The Highlight WordPress plugin before 0.9.3 does not sanitise its CustomCSS setting, allowing high privilege u

Q: How do I fix CVE-2021-24591?

highlight: upgrade to 0.9.3. Exact commands for each OS are on this page.

Q: Is CVE-2021-24591 being exploited?

CVE-2021-24591 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-2021-24591 affect?

CVE-2021-24591 affects highlight. Severity is medium (CVSS 5.4). The Highlight WordPress plugin before 0.9.3 does not sanitise its CustomCSS setting, allowing high privilege users to perform Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed

Q: How urgent is CVE-2021-24591?

Priority 36/100. Public exploit reference

Routine

MEDIUM 5.4UPGRADE

CVE-2021-24591 is a medium-severity flaw (CVSS 5.4) affecting highlight. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The Highlight WordPress plugin before 0.9.3 does not sanitise its CustomCSS setting, allowing high privilege users to perform Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.6% (top 50%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-09-06
Last modified	2026-06-17

Publisher (CNA): WPScan · Vendor: dna88

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

Am I affected?

Timeline

2021-09-06 11:15 UTCPublished CVE record published
2026-06-17 03:40 UTCUpdated Record last modified

dna88 highlight UPGRADE

Affected: < 0.9.3

Fixed in: 0.9.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy highlight || rpm -q highlight || highlight --version

2. UPGRADE to 0.9.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade highlight

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade highlight

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-2021-24591?

highlight: upgrade to 0.9.3. Exact commands for each OS are on this page.

Is CVE-2021-24591 being exploited?

CVE-2021-24591 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-2021-24591 affect?

CVE-2021-24591 affects highlight. Severity is medium (CVSS 5.4). The Highlight WordPress plugin before 0.9.3 does not sanitise its CustomCSS setting, allowing high privilege users to perform Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed

How urgent is CVE-2021-24591?

Priority 36/100. Public exploit reference

Software pages

WordPress vulnerabilities

Related CVEs

CVE-2023-33187 MEDIUM 5.4 UPGRADE Highlight is an open source, full-stack monitoring platform

References

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