Amazon Linux 2023: CVE-2023-51764: Important priority package update for postfix

Postfix through 3.8.5 allows SMTP smuggling unless configured with smtpd_data_restrictions=reject_unauth_pipelining and smtpd_discard_ehlo_keywords=chunking (or certain other options that exist in recent versions). Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Postfix supports <LF>.<CR><LF> but some other popular e-mail servers do not. To prevent attack variants (by always disallowing <LF> without <CR>), a different solution is required, such as the smtpd_forbid_bare_newline=yes option with a Postfix minimum version of 3.5.23, 3.6.13, 3.7.9, 3.8.4, or 3.9.
A flaw was found in some SMTP server configurations in Postfix. This flaw allows a remote attacker to break out email message data to "smuggle" SMTP commands and send spoofed emails that pass SPF checks.
Out of the box, Postfix targets to accommodate older clients with faulty SMTP implementations due to which restrictions are not enforced in the default configuration. Appropriate mitigation strategies are mentioned in the appropriate section below.