CVE-2026-45121

MEDIUM 4.3

MyBB: Insufficient permission check for calendar select

CVSS Score

4.3

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-863
Vendor	mybb
Product	mybb
Published	Aug 18, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Affected Versions

mybb / mybb

< 1.8.40

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/mybb/mybb/security/advisories/GHSA-r25v-7pcm-q34p github.com: https://github.com/mybb/mybb/commit/78e07fea34a6f6c326e668526bfb8e451c19e966 github.com: https://github.com/mybb/mybb/releases/tag/mybb_1840 mybb.com: https://mybb.com/versions/1.8.40