CVE-2026-45125
MyBB is free and open source forum software. Prior to 1.8.40, the Email User controller does not sanitize sender names correctly, resulting
CVSS
5.3
Medium
EPSS
0.3%
p23
KEV
—
Exploit Today
7
0-100
Published: Aug 18, 2026 · Last modified: Aug 18, 2026 · CWE-93
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.