Medium 4.3Published Aug 18, 2026

CVE-2026-45121MyBB: Insufficient permission check for calendar select

Updated under an hour ago (2026-10-19 10:10 UTC)

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Every CVE for mybb

Exploited in the last 30 days

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.

CVSS: 4.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness (CWE): CWE-863
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Aug 18, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

mybb mybb mybb:mybb (from the name)	before 1.8.40	CNA record

References

https://github.com/mybb/mybb/security/advisories/GHSA-r25v-7pcm-q34px-refsource-confirm
https://github.com/mybb/mybb/commit/78e07fea34a6f6c326e668526bfb8e451c19e966x-refsource-misc
https://github.com/mybb/mybb/releases/tag/mybb_1840x-refsource-misc
https://mybb.com/versions/1.8.40x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.