CVE-2026-45118 [CRITICAL] – MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not

MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirect target from the from HTTP parameter in $mybb->input[‘from’] or the Referer HTTP header in $_SERVER[‘HTTP_REFERER’] and passes it to redirect() without sufficient verification. A javascript: URI becomes the target of the `Click here if you don’t want to wait any longer` link because $force_redirect is true, allowing script execution when a victim selects the link. This issue is fixed in version 1.8.40.