Is CVE-2026-45125 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-45125?

CVE-2026-45125 has a CVSS v3 severity of MEDIUM (5.3).

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CVE-2026-45125

Description

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.