CVE-2026-45121: MyBB: Insufficient permission check for calendar select
MyBB is free and open source forum software. Prior to 1.8.40, the calendar module does not check permissions consistently when listing calendars, allowing authenticated users to access titles of calendars that are otherwise inaccessible. The affected calendar-selection paths in calendar.php perform permission checks against an invalid calendar context before returning calendar titles. The uniquely identifying implementation details include titles of inaccessible calendars, and invalid calendar permission context. This issue is fixed in version 1.8.40.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
MyBB calendar module (calendar.php)to a version that resolves this vulnerability.Fixed in 1.8.40
Event History
Frequently Asked Questions
Which MyBB versions are affected?
MyBB installations prior to version 1.8.40 are affected. The issue is in calendar-selection paths in calendar.php.
What access does an attacker need, and what can they obtain?
An attacker needs an authenticated MyBB account. No user interaction is required, and the disclosed impact is limited to titles of calendars the user should not be able to access.
What is the remediation?
Upgrade MyBB to version 1.8.40, which fixes the inconsistent permission checks in the calendar module.