CVE-2026-45119: Mybb

Medium severity, CVSS 4.6. EPSS: 0.2% chance of exploitation in the next 30 days.

MyBB is free and open source forum software. Prior to 1.8.40, the Admin CP UTF-8 Conversion module does not validate certain requests correctly, allowing same-site attackers to alter table encoding and deny service with a specially crafted URL. The do=all control flow in admin/modules/tools/system_health.php performs ALTER TABLE operations, column rewrite phases, and fulltext index rebuilds on GET requests for the database table named by the table parameter without request verification. The uniquely identifying implementation details include GET requests without request verification. This issue is fixed in version 1.8.40.

Affected products

• Mybb Mybb: before 1.8.40 (fixed in 1.8.40)

Published 2026-08-18. Last modified 2026-09-08.