CVE-2026-45121

MyBB: Insufficient permission check for calendar select

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.

We have discovered 1,463 live websites that are affected by CVE-2026-45121.

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Affected Software

Product  MyBB
Category Message Boards
Vulnerable Domains1,463 live websites (100% of MyBB install base)
Vulnerable Versions
  • from 0 through 1.8.40
Vulnerable Versions Count21 versions ( 100% of all versions)


Common Weakness Enumeration

CWE-863 Incorrect Authorization



Details

  • Published - Aug 18, 2026
  • Updated - Aug 18, 2026

Website Distribution by Country

Number of websites using CVE-2026-45121
United States552 websites


Germany377 websites
Poland130 websites
France76 websites
GB37 websites
Turkey25 websites
Netherlands23 websites
Italy22 websites
Iran18 websites
Russia18 websites

Website Distribution by TLD

Number of websites using CVE-2026-45121
.com535 websites
.de268 websites
.net152 websites
.org91 websites
.pl87 websites
.eu32 websites
.ru23 websites
.it18 websites
.info13 websites
.fr13 websites

Vulnerable Versions

Vulnerable versions are highlighted in red

Websites affected by CVE-2026-45121

Top websites that are affected by CVE-2026-45121. Please click on the "Contact us" link to get more information.
DomainCountryRankContacts
*********.****.com United States**,***
******.******.org United States**,***
*****.****.tv United States***,***
********.pl Poland***,***
*************.org Laos***,***
*************.net United States***,***
************.pl Poland***,***
********.net United States***,***
**********.org United States***,***
*******.com United States***,***
See full domain list

FAQ

CVE-2026-45121 is Incorrect Authorization in MyBB
A total of 1,463 websites have been identified as vulnerable to CVE-2026-45121, based on global website indexing conducted by WebTechSurvey.
The MyBB is affected by the CVE-2026-45121 vulnerability.
MyBB versions up to 1.8.40 are vulnerable to CVE-2026-45121.
CVE-2026-45121 is resolved in version 1.8.40 of MyBB.