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

Q: What is CVE-2021-39318?

CVE-2021-39318 is a medium-severity cross-site scripting vulnerability in H5P CSS Editor, published on 14 Dec 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Q: Is CVE-2021-39318 being exploited?

There is no known exploitation of CVE-2021-39318 in the wild and no public exploit code.

Q: How do I fix CVE-2021-39318?

No fix has been published for CVE-2021-39318 yet. Limit exposure of the affected software until one is available.

Medium 6.1 Published 14 Dec 2021 Updated 13 Feb 2025

Attackers can inject arbitrary web scripts via the h5p-css-file parameter in the H5P CSS Editor WordPress plugin, potentially compromising user sessions.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2021-39318?

CVE-2021-39318 is a medium-severity cross-site scripting vulnerability in H5P CSS Editor, published on 14 Dec 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-79

Which versions are affected by CVE-2021-39318?

It affects 1 product.

Products include H5p-Css-Editor Project H5p-Css-Editor.

How do I fix CVE-2021-39318?

No fix has been published for CVE-2021-39318 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2021-39318 being exploited?