CVE-2021-39338: Mybb Cross-Poster Project Mybb Cross-Poster

Medium severity, CVSS 4.8. EPSS: 0.9% chance of exploitation in the next 30 days.

The MyBB Cross-Poster WordPress plugin is vulnerable to Stored Cross-Site Scripting due to insufficient input validation and sanitization via several parameters found in the ~/classes/MyBBXPSettings.php file which allowed attackers with administrative user access to inject arbitrary web scripts, in versions up to and including 1.0. This affects multi-site installations where unfiltered_html is disabled for administrators, and sites where unfiltered_html is disabled.

Affected products

• Mybb Cross-Poster Project Mybb Cross-Poster: up to and including 1.0

Published 2021-10-15. Last modified 2026-06-17.