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Vulnerability · Published Aug 18, 2026 · Assigned by GitHub_M

CVE-2026-45122MyBB: Insufficient permission check for calendar event move

Medium 4.3

In plain English

A medium-severity incorrect authorization 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 27% of all known vulnerabilities).

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.3%top 72.9% 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 validate moderation permissions for the destination calendar when moving events. A user with moderation permission for the source calendar can move an event to a calendar where the user has only viewing permission because the do_move action in calendar.php does not check canmoderateevents for the target calendar. The uniquely identifying implementation details include calendar event move, source calendar moderation permission, and destination calendar viewing permission. This issue is fixed in version 1.8.40.

Affected products (as reported)

VendorProductVersions
mybb mybb < 1.8.40

Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

References