---
id: CVE-2026-45117
title: MyBB is free and open source forum software
summary: >-
  MyBB is free and open source forum software. From 1.8.13 until 1.8.40, the
  installer module does not properly escape user-supplied database configuration
  values written to the configuration file, resulting in PHP code injection and
  remot…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-94
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-2026-45117'
references:
  - url: >-
      https://github.com/mybb/mybb/commit/0fe713e3b964bfc878ea65bdd9f746f585f6ebbf
    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-gpc4-77rp-3xqr'
    label: security-advisories@github.com
  - url: 'https://mybb.com/versions/1.8.40'
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.01149
epssPercentile: 0.65451
ingestedAt: '2026-09-08T21:11:12.280Z'
---

## Overview

MyBB is free and open source forum software. From 1.8.13 until 1.8.40, the installer module does not properly escape user-supplied database configuration values written to the configuration file, resulting in PHP code injection and remote code execution when the installer is available. install/index.php processes the values with addcslashes(), but the $characters argument added in MyBB 1.8.13 does not include the backslash character, allowing crafted input to escape the generated PHP string. The uniquely identifying implementation details include introduced in MyBB 1.8.13. This issue is fixed in version 1.8.40.

## Remediation

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