Stored JavaScript Code Injection in MyBB Forum Software
CVE-2026-45116

8.7HIGH

Key Information:

Vendor

Mybb

Status
Mybb
Vendor
CVE Published:
18 August 2026

What is CVE-2026-45116?

MyBB, an open-source forum software, is affected by a vulnerability that allows for stored JavaScript code injection due to improper validation of checkbox and multiselect profile field types. Specifically, the user datahandler does not verify the intended structure of profile_fields, which can lead to user-controlled data being stored unvalidated. This unverified input can be rendered directly on pages, exposing the application to XSS (Cross-Site Scripting) attacks. The issue has been resolved in version 1.8.40.

Affected Version(s)

mybb < 1.8.40

References

https://github.com/mybb/mybb/security/advisories/GHSA-4p6...
x_refsource_CONFIRM
https://github.com/mybb/mybb/commit/c32f0c22baab704a68b8d...
x_refsource_MISC
https://github.com/mybb/mybb/releases/tag/mybb_1840
x_refsource_MISC

CVSS V3.1

Score:
8.7
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
Required
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.