Vulnerability · Published Aug 18, 2026 · Assigned by GitHub_M

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

Medium 5.4

In plain English

A medium-severity authorization bypass via user-controlled key in mybb from mybb. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities).

Severity (CVSS 3.1)5.4Medium

Exploit odds (30 days)0.3%top 76.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 (as reported)

Vendor	Product	Versions
mybb	mybb	< 1.8.40

Weakness: CWE-639 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

References

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