CVE-2026-45122
Received Received - Intake

Calendar Event Move Permission Bypass in MyBB

Publication date: 2026-08-18

Last updated on: 2026-08-18

Assigner: GitHub, Inc.

Description
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.

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Meta Information

Published
2026-08-18
Last Modified
2026-08-18
Generated
2026-09-08
AI Q&A
2026-08-18
EPSS Evaluated
2026-09-07
NVD
CVE-2026-45122
EUVD
EUVD-2026-61010

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
mybb mybb 1.8.40

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-863 The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

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Executive Summary

This vulnerability affects MyBB forum software versions before 1.8.40. It involves insufficient permission checks when moving calendar events. A user with moderation rights for a source calendar can move events to a destination calendar where they only have viewing permissions, bypassing proper authorization.

Detection Guidance

To detect this vulnerability, check if your MyBB installation is running a version prior to 1.8.40. Use the command: grep -r "1.8.3" /path/to/mybb/ to search for outdated versions. Additionally, review calendar event move logs for unauthorized event movements between calendars.

Impact Analysis

An attacker with moderation access to one calendar could move events to another calendar where they lack moderation rights. This could disrupt event organization or expose sensitive information if events are moved to less secure locations.

Compliance Impact

This vulnerability may impact compliance by allowing unauthorized changes to event locations, potentially violating data integrity or access control requirements in GDPR or HIPAA. However, no specific compliance impact is detailed in the provided context.

Mitigation Strategies

Immediately upgrade MyBB to version 1.8.40 or later. If upgrading is not possible, apply the patch from the GitHub commit 86ed2058e7f9a2c14828e731f684e997f9bb220c to add the required permission check in calendar.php.

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