Strategic Overview
- Status
- Unpatched
- Affected Plugin
- H5P CSS Editor
- Affected Version
<= 1.0- CVSS
- 6.1Medium
- Weakness type
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
- CVE
CVE-2021-39318
At a glance
CVE-2021-39318 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the H5P CSS Editor WordPress plugin, affecting versions <= 1.0. It carries a CVSS score of 6.1 (reachable over the network; low attack complexity). Exploitation requires no authentication. No fixed release has been reported yet; treat installations running this software as exposed. Disclosed December 2021, reported by p7e4.
Vulnerability Overview
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.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site.
CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Reaching this weakness in H5P CSS Editor <= 1.0 takes a caller who can reach the endpoint. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.
Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. No fixed build of this plugin is recorded for H5P CSS Editor yet, so installs running <= 1.0 stay exposed until the vendor ships one.
Remediation
No known patch available. Please review the vulnerability's details in depth and employ mitigations based on your organization's risk tolerance. It may be best to uninstall the affected software and find a replacement.
How does WordSec protect against this?
The attempt arrives as an ordinary request to H5P CSS Editor: WordSec's web application firewall inspects request payloads before WordPress loads them. No patched version is recorded yet, which is the case where a filtering layer matters most, because there is nothing to update to.
- Firewall
- Alerts
External References
Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C