[pmg-devel] [PATCH pmg-api 1/2] templates: postfix: adapt to current default setting for smtpsmuggling

[Stoiko Ivanov <s.ivanov@proxmox.com>]

postfix recently released new versions (for all supported stable
versions including 3.7.10), which changed the behavior regarding bare
newlines (which originally caused smtp-smuggling [0]).

Instead of directly rejecting smtp sessions when <LF> is used as
command separator, the session continues, however a bare <LF> is not
recognized as end for the DATA command.

The current setting of `smtpd_forbid_bare_newline = yes` (in 3.7.9)
used to behave like the new setting of 'reject'. In 3.7.10 this was
changed and it behaves like `smtpd_forbid_bare_newline = normalize`
(the default for postfix > 3.9)

The current patch simply adapts to the current default naming (yes is
an alias for normalize) - The change in behavior came with the postfix
update shipped in proposed-updates end of January and part of Debian
12.5 (released on 10.02.2024).

As both versions mitigate smtp-smuggling in postfix, and even the more
drastic behavior of rejecting bare <LF> did not cause any problems in
our support-channels and own deployments the patch is not
security-relevant.

[0] https://www.postfix.org/smtp-smuggling.html
[1] https://metadata.ftp-master.debian.org/changelogs//main/p/postfix/postfix_3.7.10-0+deb12u1_changelog

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
---
 src/templates/main.cf.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/templates/main.cf.in b/src/templates/main.cf.in
index 3b56355..e686884 100644
--- a/src/templates/main.cf.in
+++ b/src/templates/main.cf.in
@@ -101,7 +101,7 @@ unverified_recipient_reject_code = [% pmg.mail.verifyreceivers %]
 
 smtpd_data_restrictions = reject_unauth_pipelining
 
-smtpd_forbid_bare_newline = yes
+smtpd_forbid_bare_newline = normalize
 smtpd_forbid_bare_newline_exclusions =
         $mynetworks,
         cidr:/etc/postfix/clientaccess
-- 
2.39.2