CVE-2026-45120
Received Received - Intake

Information Disclosure in MyBB Calendar Module

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 verify private event status consistently, allowing users with viewing and moderation permissions to access and moderate private events. The private-event check used by get_events() in inc/functions_calendar.php and the event action is missing from the remaining calendar.php actions, despite the limited-access behavior described in inc/languages/english/calendar.lang.php. 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
2026-09-07
AI Q&A
2026-08-18
EPSS Evaluated
2026-09-06
NVD
CVE-2026-45120
EUVD
EUVD-2026-61017

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
mybb mybb to 1.8.40 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-639 The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

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Executive Summary

This vulnerability in MyBB forum software prior to version 1.8.40 allows users with viewing and moderation permissions to access and moderate private events without proper verification. The calendar module fails to consistently check private event status, leading to unauthorized access despite the intended limited-access behavior.

Detection Guidance

To detect this vulnerability, check if your MyBB installation is running version 1.8.40 or later. If not, the calendar module may be vulnerable. Review calendar event access logs for unauthorized access to private events by users with viewing or moderation permissions.

Impact Analysis

If you use MyBB versions before 1.8.40, attackers with moderation rights could view or modify private events they should not access. This could expose sensitive information or disrupt event management on your forum.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by allowing unauthorized access to private calendar events. If private events contain sensitive personal data, the lack of proper authorization checks may violate data protection requirements for confidentiality and access controls.

Mitigation Strategies

Immediately upgrade MyBB to version 1.8.40 or later to patch the vulnerability. Review and restrict user permissions to ensure only authorized users can access private events. Monitor calendar module activity for suspicious behavior.

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