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.

Classification

CVE ID: CVE-2025-48940

CVSS Base Severity: HIGH

CVSS Base Score: 7.2

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

Affected Products

Vendor: mybb

Product: mybb

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.05% (probability of being exploited)

EPSS Percentile: 15.96% (scored less or equal to compared to others)

EPSS Date: 2025-06-03 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-48940
https://github.com/mybb/mybb/security/advisories/GHSA-q4jv-xwjx-37cp
https://github.com/mybb/mybb/commit/6e6cfbd524d9101b51e1278ecf520479b64b0f00
https://mybb.com/versions/1.8.39

Timeline