CVE-2026-45121 MyBB: Insufficient permission check for calendar select
Authenticated users can view titles of inaccessible calendars due to insufficient permission checks in the MyBB forum software.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-45121?
CVE-2026-45121 is a medium-severity missing authorization vulnerability in mybb, published on 18 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Weakness: CWE-863
Which versions are affected by CVE-2026-45121?
How do I fix CVE-2026-45121?
No fix has been published for CVE-2026-45121 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-45121 being exploited?
There is no known exploitation of CVE-2026-45121 in the wild and no public exploit code.
Sources
Also known as GHSA-r25v-7pcm-q34p.