CVE-2026-45121

4.3 mediumEPSS 0.3%

Medium (4.3). EPSS 0.3% chance of exploitation in the next 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.

Severity

CVSS 3.1

4.3 medium

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

EPSS: 0.3% chance of exploitation in the next 30 days; higher than 27% of CVEs (scores of 2026-10-31)
CWE: CWE-863
Published: 2026-08-18
Modified: 2026-09-08
Record from: the NVD, synced 2026-10-19

References

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

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