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Fencer Intel
medium 5.4

CVE-2026-45120 json

MyBB: Insufficient authorization for private calendar events

published 2mo ago modified 2mo ago also EUVD-2026-61017

cvss
5.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 23%
public exploits
0
none known

Summary

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.

Patch / fix

  • mybb mybb 1.8.40

Is CVE-2026-45120 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2mo ago

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Affected products

  • mybb mybb

Classification

Weakness
  • CWE-639 Authorization Bypass Through User-Controlled Key

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.