CVE-2026-45121

What it is

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.

At a glance

Exploitability

Can be exploited over the network with a low-privilege account. Limited direct impact.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-18 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-08 21:02 UTC Last updatedMost recent change to the record

Details

Published

2026-08-18 16:17 UTC

Last modified

2026-09-08 21:02 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-863 · Incorrect authorization

Record status

Deferred

Attack profile CVSS 3.1 · 4.3

Attack vector

Network

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None