CVE-2026-45127: MyBB: ACP Mass Mail draft resend CSRF
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 mybbmassemails.status set to 0 on GET requests without request forgery protection. The uniquely identifying implementation details include Users & Groups → Mass Mail → Mass Mailing Archive, mybbmassemails.status = 0, and admin/modules/user/massmail.php. This issue is fixed in version 1.8.40.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
MyBBto a version that resolves this vulnerability.Fixed in 1.8.40
Event History
Frequently Asked Questions
Who is exposed to this issue?
MyBB installations prior to 1.8.40 are affected where an attacker can cause an authenticated Admin CP user to visit a specially crafted URL. The issue is in the Admin CP Mass Mail archive resend functionality.
What does an attacker need to exploit it?
Exploitation requires low-privileged access and user interaction. A same-site attacker must induce an authenticated administrator to load the crafted GET request; the request can then duplicate an archived mailing entry as a new draft.
What is the remediation?
Upgrade MyBB to version 1.8.40, which fixes the missing request-forgery protection on the affected resend route.
How can I identify possible exploitation?
Review the Admin CP Mass Mailing Archive and look for unexpected draft entries. Affected drafts are created from archived mailings with mybb_massemails.status set to 0.