MyBB up to 1.8.39 Calendar calendar.php do_move permission

Summaryinfo

A vulnerability classified as critical has been found in MyBB up to 1.8.39. Impacted is the function do_move of the file calendar.php of the component Calendar Module. Performing a manipulation results in permission. This vulnerability was named CVE-2026-45122. The attack may be initiated remotely. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in MyBB up to 1.8.39. It has been classified as critical. This affects the function do_move of the file calendar.php of the component Calendar Module. The manipulation with an unknown input leads to a permission vulnerability. CWE is classifying the issue as CWE-275. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-45122 since 05/08/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/18/2026). The attack technique deployed by this issue is T1222 according to MITRE ATT&CK.

By approaching the search of inurl:calendar.php it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 1.8.40 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Content Management System

Name

• MyBB

Version

• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5
• 1.8.6
• 1.8.7
• 1.8.8
• 1.8.9
• 1.8.10
• 1.8.11
• 1.8.12
• 1.8.13
• 1.8.14
• 1.8.15
• 1.8.16
• 1.8.17
• 1.8.18
• 1.8.19
• 1.8.20
• 1.8.21
• 1.8.22
• 1.8.23
• 1.8.24
• 1.8.25
• 1.8.26
• 1.8.27
• 1.8.28
• 1.8.29
• 1.8.30
• 1.8.31
• 1.8.32
• 1.8.33
• 1.8.34
• 1.8.35
• 1.8.36
• 1.8.37
• 1.8.38
• 1.8.39

License

• open-source

Website

• Product: https://mybb.com/

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