NGINX Open Source and NGINX Plus have a vulnerability in the
ngx_mail_smtp_module that might allow an unauthenticated attacker to
over-read NGINX SMTP authentication process memory; as a result, the
server side may leak arbitrary bytes sent in a request to the
authentication server. This issue happens during the NGINX SMTP
authentication process and requires the attacker to make preparations
against the target system to extract the leaked data. The issue
affects NGINX only if (1) it is built with the ngx_mail_smtp_module,
(2) the smtp_auth directive is configured with method "none,"
and (3) the authentication server returns the "Auth-Wait" response
header.