CVE-2026-45116

HIGH 8.7

MyBB: Profile field type confusion XSS

CVSS Score

8.7

EPSS Score

0.0%

EPSS Percentile

0th

MyBB is free and open source forum software. Prior to 1.8.40, the user datahandler does not properly validate checkbox and multiselect profile field types, resulting in stored JavaScript code injection. UserDataHandler::verify_profile_fields() only performs the specialized validation when is_array($profile_fields[$field]) is true. A non-array profile_fields[fidX] value instead of the expected profile_fields[fidX][] shape falls through to generic text handling and is stored without verification. The affected value is then rendered directly by member.php and inc/functions_post.php rather than processed by the MyCode parser. The uniquely identifying implementation details include inc/datahandlers/user.php. This issue is fixed in version 1.8.40.

CWE	CWE-79
Vendor	mybb
Product	mybb
Published	Aug 18, 2026
Last Updated	Aug 18, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

High

Availability

None

Affected Versions

mybb / mybb

< 1.8.40

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/mybb/mybb/security/advisories/GHSA-4p6g-p3qh-559v github.com: https://github.com/mybb/mybb/commit/c32f0c22baab704a68b8d58fcdd2f26fadbbe19b github.com: https://github.com/mybb/mybb/releases/tag/mybb_1840 mybb.com: https://mybb.com/versions/1.8.40