How severe is CVE-2020-4070?

CVE-2020-4070 has a CVSS 3.x base score of 4.6, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2020-4070 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-4070?

CVE-2020-4070 affects W3c Css Validator. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2020-4070?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2020-4070 published?

CVE-2020-4070 was published on 2020-06-22 and last updated on 2026-06-17.

CVE-2020-4070

CVE-2020-4070 is a medium-severity vulnerability in W3c Css Validator with a CVSS 3.x base score of 4.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 4.6)
CVSS v2: 3.5
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: W3c Css Validator
Published: 2020-06-22
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2020-4070?: 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.
How severe is CVE-2020-4070?: CVE-2020-4070 has a CVSS 3.x base score of 4.6, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2020-4070 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-4070?: CVE-2020-4070 affects W3c Css Validator. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2020-4070?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2020-4070 published?: CVE-2020-4070 was published on 2020-06-22 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:w3c:css_validator:*:*:*:*:*:*:*:*

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