Auth bypass in Mybb
CVE-2026-45122
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.
Vulnerability class: Broken Access Control
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.
Affected products
- Mybb — versions < 1.8.40
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-45122?
- CVE-2026-45122 is a medium-severity vulnerability in Mybb, classified under Incorrect Authorization. CVSS score: 4.3/10. Published 2026-08-18.
- How severe is CVE-2026-45122?
- Medium severity. CVSS v3 base score is 4.3 out of 10.