Description
MyBB is free and open source forum software. Prior to version 1.8.39, the upgrade component does not validate user input properly, which allows attackers to perform local file inclusion (LFI) via a specially crafted parameter value. In order to exploit the vulnerability, the installer must be unlocked (no `install/lock` file present) and the upgrade script must be accessible (by re-installing the forum via access to `install/index.php`; when the forum has not yet been installed; or the attacker is authenticated as a forum administrator). MyBB 1.8.39 resolves this issue.
References (3)
Core 3
Core References
Vendor Advisory x_refsource_confirm
https://github.com/mybb/mybb/security/advisories/GHSA-q4jv-xwjx-37cp
Patch x_refsource_misc
https://github.com/mybb/mybb/commit/6e6cfbd524d9101b51e1278ecf520479b64b0f00
Product, Release Notes x_refsource_misc
https://mybb.com/versions/1.8.39
Scores
CVSS v3
7.2
EPSS
0.0050
EPSS Percentile
66.3%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
no
Technical Impact
partial
Details
CWE
CWE-22
Status
published
Products (1)
mybb/mybb
< 1.8.39
Published
Jun 02, 2025
Tracked Since
Feb 18, 2026