Vulnerability · Published Aug 18, 2026 · Assigned by GitHub_M

CVE-2026-45127MyBB: ACP Mass Mail draft resend CSRF

Low 3.5

In plain English

A low-severity cross-site request forgery in mybb from mybb. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities).

Severity (CVSS 3.1)3.5Low

Exploit odds (30 days)0.2%top 93.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
mybb	mybb	< 1.8.40

Weakness: CWE-352 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N

References

https://github.com/mybb/mybb/security/advisories/GHSA-xx78-g79m-qvgq x_refsource_CONFIRM
https://github.com/mybb/mybb/commit/a95c5d6730b943adab7e54bc209c051f98843a3b x_refsource_MISC
https://github.com/mybb/mybb/releases/tag/mybb_1840 x_refsource_MISC
https://mybb.com/versions/1.8.40 x_refsource_MISC