CVE-2026-45125

MEDIUM 5.3

MyBB: Email User CRLF injection

CVSS Score

5.3

EPSS Score

0.0%

EPSS Percentile

0th

MyBB is free and open source forum software. Prior to 1.8.40, the Email User controller does not sanitize sender names correctly, resulting in mail header injection. member.php?action=do_emailuser accepts the fromname HTTP parameter for guests or the stored username for authenticated users when the cansendemail group permission is enabled. When mail_handler is set to the default PHP mail value, the sender name is used without sanitization in Return-Path and Reply-To headers, allowing arbitrary headers to be injected with CRLF sequences. This issue is fixed in version 1.8.40.

CWE	CWE-93
Vendor	mybb
Product	mybb
Published	Aug 18, 2026
Last Updated	Aug 18, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Affected Versions

mybb / mybb

< 1.8.40

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/mybb/mybb/security/advisories/GHSA-f626-53q9-pqm9 github.com: https://github.com/mybb/mybb/commit/5046c56b515d4593297a4f65b0c6ccb0b55baa01 github.com: https://github.com/mybb/mybb/releases/tag/mybb_1840 mybb.com: https://mybb.com/versions/1.8.40