CVE-2020-4070: In CSS Validator less than or equal to commit 54d68a1, there is a cross-site scripting vulnerability in handli

Q: How do I fix CVE-2020-4070?

css validator: upgrade to newer than 2020-01-19. Exact commands for each OS are on this page.

Q: Is CVE-2020-4070 being exploited?

CVE-2020-4070 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-2020-4070 affect?

CVE-2020-4070 affects css validator. Severity is medium (CVSS 4.6). In CSS Validator less than or equal to commit 54d68a1, there is a cross-site scripting vulnerability in handling URIs. A user would have to click on a specifically crafted validator link to trigger it. This has been patched in commit e5c09a

Q: How urgent is CVE-2020-4070?

Priority 28/100. No elevated risk signals yet.

Routine

MEDIUM 4.6UPGRADE

CVE-2020-4070 is a medium-severity flaw (CVSS 4.6) affecting css validator. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In CSS Validator less than or equal to commit 54d68a1, there is a cross-site scripting vulnerability in handling URIs. A user would have to click on a specifically crafted validator link to trigger it. This has been patched in commit e5c09a9.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.6 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.5% (top 54%)
CISA exploited list	No
Weakness	CWE-79
Published	2020-06-22
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: w3c

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

Am I affected?

Timeline

2020-06-22 16:15 UTCPublished CVE record published
2026-06-17 03:19 UTCUpdated Record last modified

w3c css validator UPGRADE

Affected: <= 2020-01-19

Fixed in: newer than 2020-01-19

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy css-validator || rpm -q css-validator || css-validator --version

2. UPGRADE to newer than 2020-01-19 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade css-validator

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade css-validator

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-2020-4070?

css validator: upgrade to newer than 2020-01-19. Exact commands for each OS are on this page.

Is CVE-2020-4070 being exploited?

CVE-2020-4070 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-2020-4070 affect?

CVE-2020-4070 affects css validator. Severity is medium (CVSS 4.6). In CSS Validator less than or equal to commit 54d68a1, there is a cross-site scripting vulnerability in handling URIs. A user would have to click on a specifically crafted validator link to trigger it. This has been patched in commit e5c09a

How urgent is CVE-2020-4070?

Priority 28/100. No elevated risk signals yet.

Related CVEs

CVE-2025-1781 MEDIUM 6.5 UPGRADE There is a XXE in W3CSS Validator versions before cssval-20250226 that allows an attacker to use specially-cra

References

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