---
id: CVE-2026-45116
title: MyBB is free and open source forum software
summary: >-
  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_fi…
severity: high
cvss: 8.7
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N'
cwe:
  - CWE-79
published: '2026-08-18'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T21:02:26.047'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-45116'
references:
  - url: >-
      https://github.com/mybb/mybb/commit/c32f0c22baab704a68b8d58fcdd2f26fadbbe19b
    label: security-advisories@github.com
  - url: 'https://github.com/mybb/mybb/releases/tag/mybb_1840'
    label: security-advisories@github.com
  - url: 'https://github.com/mybb/mybb/security/advisories/GHSA-4p6g-p3qh-559v'
    label: security-advisories@github.com
  - url: 'https://mybb.com/versions/1.8.40'
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.0043
epssPercentile: 0.34514
ingestedAt: '2026-09-08T21:11:12.280Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.