CVE-2026-45120: MyBB: Insufficient authorization for private calendar events

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-18 · updated 2026-09-08
Weakness: CWE-639

Description

MyBB is free and open source forum software. Prior to 1.8.40, the calendar module does not verify private event status consistently, allowing users with viewing and moderation permissions to access and moderate private events. The private-event check used by get_events() in inc/functions_calendar.php and the event action is missing from the remaining calendar.php actions, despite the limited-access behavior described in inc/languages/english/calendar.lang.php. This issue is fixed in version 1.8.40.

Affected products

mybb: before 1.8.40

References

https://github.com/mybb/mybb/commit/c077e6c29755187c4df78a1e674dd61bc55701b3
https://github.com/mybb/mybb/releases/tag/mybb_1840
https://github.com/mybb/mybb/security/advisories/GHSA-c2hm-g9w6-pv6x
https://mybb.com/versions/1.8.40

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