Postfix SMTP Smuggling – Expect Script POC

send an email that is legitimate, but inside the email there is many others emails (different senders, recipients, subjet, etc). The initial email is check for SPF/DKIM/DMARC, the others inside are not !

usage: ./cve-2023-51764.sh mx.fqdn port
./cve-2023-51764.sh mail.mydomain.com 25

Postfix through 3.8.4 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: 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.