CVE-2026-45127

What it is

MyBB is free and open source forum software. Prior to 1.8.40, the ACP Mass Mail module does not validate certain requests correctly, allowing same-site attackers to create draft entries from archived entries by embedding a specially crafted URL. The Resend route in Admin CP, Users & Groups, Mass Mail, Mass Mailing Archive duplicates archived mailing entries into new drafts with mybb_massemails.status set to 0 on GET requests without request forgery protection. The uniquely identifying implementation details include Users & Groups → Mass Mail → Mass Mailing Archive, mybb_massemails.status = 0, and admin/modules/user/mass_mail.php. This issue is fixed in version 1.8.40.

At a glance

Exploitability

Can be exploited over the network with a low-privilege account, but needs a user to act. Limited direct impact.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-18 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-08 21:02 UTC Last updatedMost recent change to the record

Details

Published

2026-08-18 16:17 UTC

Last modified

2026-09-08 21:02 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-352 · Cross-site request forgery

Record status

Deferred

Attack profile CVSS 3.1 · 3.5

Attack vector

Network

Complexity

Low

Privileges needed

Low

User interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None