CVE-2021-39338 : Security Advisory and Response

The MyBB Cross-Poster WordPress plugin has a vulnerability allowing Stored Cross-Site Scripting, affecting versions up to and including 1.0.

Understanding CVE-2021-39338

This CVE details an Authenticated Stored Cross-Site Scripting vulnerability in the MyBB Cross-Poster plugin.

What is CVE-2021-39338?

The vulnerability in the MyBB Cross-Poster plugin allows attackers with administrative user access to inject arbitrary web scripts due to inadequate input validation.

The Impact of CVE-2021-39338

The impact is rated as MEDIUM severity with a CVSS base score of 5.5. It affects multi-site installations with disabled unfiltered_html for administrators.

Technical Details of CVE-2021-39338

This section covers specific technical details of the vulnerability.

Vulnerability Description

The issue arises from insufficient input validation in several parameters within the MyBBXPSettings.php file.

Affected Systems and Versions

Product: MyBB Cross-Poster
Vendor: MyBB Cross-Poster
Versions Affected: <= 1.0

Exploitation Mechanism

Attackers with administrative user access can exploit the vulnerability to insert malicious web scripts.

Mitigation and Prevention

Steps to address and prevent the vulnerability.

Immediate Steps to Take

Uninstall the MyBB Cross-Poster plugin from your WordPress site.

Long-Term Security Practices

Regularly update plugins to ensure vulnerabilities are patched promptly.
Consider implementing additional security measures such as web application firewalls.
Educate administrators on best practices for handling user inputs.
Monitor for unusual activities in the system.

Patching and Updates

Keep all software, including plugins and WordPress itself, up to date to mitigate potential security risks.