What’s Vulnerable › Vulnerabilities

CVE-2021-39318: H5P CSS Editor <= 1.0 Reflected Cross-Site Scripting

• Severity: medium (CVSS 4.3 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-12-14 · updated 2026-06-17
• Weakness: CWE-79

Description

The H5P CSS Editor WordPress plugin is vulnerable to Reflected Cross-Site Scripting via the h5p-css-file parameter found in the ~/h5p-css-editor.php file which allows attackers to inject arbitrary web scripts, in versions up to and including 1.0.

Affected products

• H5P CSS Editor: through 1.0

References

• https://plugins.trac.wordpress.org/browser/h5p-css-editor/tags/1.0/h5p-css-editor.php#L50
• https://www.wordfence.com/vulnerability-advisories/#CVE-2021-39318
• https://plugins.trac.wordpress.org/browser/h5p-css-editor/tags/1.0/h5p-css-editor.php#L50
• https://www.wordfence.com/vulnerability-advisories/#CVE-2021-39318

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