Upgrade TLS settings

CHANGELOG.md

@@ -4,6 +4,10 @@ CHANGELOG
 Under Development
 -----------------
 
+System:
+
+* TLS settings have been upgraded following Mozilla's recommendations for servers. TLS1.2 and 1.3 are now the only supported protocols for web, IMAP, and SMTP (submission).
+
 WebMail:
 * Set the default Roundcube skin to the new "Elastic" theme.
 

conf/nginx-ssl.conf

@@ -1,7 +1,7 @@
 # We track the Mozilla "intermediate" compatibility TLS recommendations.
 # Note that these settings are repeated in the SMTP and IMAP configuration.
 # ssl_protocols has moved to nginx.conf in bionic, check there for enabled protocols.
-ssl_ciphers 'ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS';
+ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384;
 ssl_dhparam STORAGE_ROOT/ssl/dh2048.pem;
 
 # as recommended by http://nginx.org/en/docs/http/configuring_https_servers.html

security.md

@@ -39,9 +39,9 @@ These services are protected by [TLS](https://en.wikipedia.org/wiki/Transport_La
 The services all follow these rules:
 
 * TLS certificates are generated with 2048-bit RSA keys and SHA-256 fingerprints. The box provides a self-signed certificate by default. The [setup guide](https://mailinabox.email/guide.html) explains how to verify the certificate fingerprint on first login. Users are encouraged to replace the certificate with a proper CA-signed one. ([source](setup/ssl.sh))
-* Only TLSv1, TLSv1.1 and TLSv1.2 are offered (the older SSL protocols are not offered).
+* Only TLSv1.2+ are offered (the older SSL protocols are not offered).
-* HTTPS, IMAP, and POP track the [Mozilla Intermediate Ciphers Recommendation](https://wiki.mozilla.org/Security/Server_Side_TLS), balancing security with supporting a wide range of mail clients. Diffie-Hellman ciphers use a 2048-bit key for forward secrecy. For more details, see the [output of SSLyze for these ports](tests/tls_results.txt).
+* We track the [Mozilla Intermediate Ciphers Recommendation](https://wiki.mozilla.org/Security/Server_Side_TLS), balancing security with supporting a wide range of mail clients. Diffie-Hellman ciphers use a 2048-bit key for forward secrecy. For more details, see the [output of SSLyze for these ports](tests/tls_results.txt).
-* SMTP (port 25) uses the Postfix medium grade ciphers and SMTP Submission (port 587) uses the Postfix high grade ciphers ([more info](http://www.postfix.org/postconf.5.html#smtpd_tls_mandatory_ciphers)).
+* SMTP port 25 (inbound) follows similar rules. Outbound SMTP (i.e. the server is the client) uses more relaxed settings.
 
 Additionally:
 

setup/mail-dovecot.sh

@@ -78,16 +78,15 @@ tools/editconf.py /etc/dovecot/conf.d/10-auth.conf \
 	"auth_mechanisms=plain login"
 
 # Enable SSL, specify the location of the SSL certificate and private key files.
-# Disable obsolete SSL protocols and allow only good ciphers per http://baldric.net/2013/12/07/tls-ciphers-in-postfix-and-dovecot/.
+# Use Mozilla's "Intermediate" recommendations at https://ssl-config.mozilla.org/#server=dovecot&server-version=2.2.33&config=intermediate&openssl-version=1.1.1,
-# Enable strong ssl dh parameters
+# except that the current version of Dovecot does not have a TLSv1.3 setting, so we only use TLSv1.2.
-
 tools/editconf.py /etc/dovecot/conf.d/10-ssl.conf \
 	ssl=required \
 	"ssl_cert=<$STORAGE_ROOT/ssl/ssl_certificate.pem" \
 	"ssl_key=<$STORAGE_ROOT/ssl/ssl_private_key.pem" \
-	"ssl_protocols=!SSLv3" \
+	"ssl_protocols=TLSv1.2" \
-	"ssl_cipher_list=ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS" \
+	"ssl_cipher_list=ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384" \
-	"ssl_prefer_server_ciphers=yes" \
+	"ssl_prefer_server_ciphers=no" \
 	"ssl_dh_parameters_length=2048"
 
 # Disable in-the-clear IMAP/POP because there is no reason for a user to transmit

setup/mail-postfix.sh

@@ -80,7 +80,6 @@ tools/editconf.py /etc/postfix/main.cf \
 #   OpenDKIM milter only. See dkim.sh.
 # * Even though we dont allow auth over non-TLS connections (smtpd_tls_auth_only below, and without auth the client cant
 #   send outbound mail), don't allow non-TLS mail submission on this port anyway to prevent accidental misconfiguration.
-# * Require the best ciphers for incoming connections per http://baldric.net/2013/12/07/tls-ciphers-in-postfix-and-dovecot/.
 #   By putting this setting here we leave opportunistic TLS on incoming mail at default cipher settings (any cipher is better than none).
 # * Give it a different name in syslog to distinguish it from the port 25 smtpd server.
 # * Add a new cleanup service specific to the submission service ('authclean')
@@ -93,7 +92,6 @@ tools/editconf.py /etc/postfix/master.cf -s -w \
 	  -o syslog_name=postfix/submission
 	  -o smtpd_milters=inet:127.0.0.1:8891
 	  -o smtpd_tls_security_level=encrypt
-	  -o smtpd_tls_ciphers=high -o smtpd_tls_exclude_ciphers=aNULL,DES,3DES,MD5,DES+MD5,RC4 -o smtpd_tls_mandatory_protocols=!SSLv2,!SSLv3
 	  -o cleanup_service_name=authclean" \
 	"authclean=unix  n       -       -       -       0       cleanup
 	  -o header_checks=pcre:/etc/postfix/outgoing_mail_header_filters
@@ -111,17 +109,23 @@ sed -i "s/PUBLIC_IP/$PUBLIC_IP/" /etc/postfix/outgoing_mail_header_filters
 # Enable TLS on these and all other connections (i.e. ports 25 *and* 587) and
 # require TLS before a user is allowed to authenticate. This also makes
 # opportunistic TLS available on *incoming* mail.
-# Set stronger DH parameters, which via openssl tend to default to 1024 bits
+# Set stronger DH parameters, which via openssl tend to default to 1024 bits.
-# (see ssl.sh).
+# Use Mozilla's "Intermediate" TLS recommendations from https://ssl-config.mozilla.org/#server=postfix&server-version=3.3.0&config=intermediate&openssl-version=1.1.1
+# (but use and override the "high" cipher list so we don't conflict with the
+# more permissive settings for outgoing mail).
 tools/editconf.py /etc/postfix/main.cf \
 	smtpd_tls_security_level=may\
 	smtpd_tls_auth_only=yes \
 	smtpd_tls_cert_file=$STORAGE_ROOT/ssl/ssl_certificate.pem \
 	smtpd_tls_key_file=$STORAGE_ROOT/ssl/ssl_private_key.pem \
 	smtpd_tls_dh1024_param_file=$STORAGE_ROOT/ssl/dh2048.pem \
-	smtpd_tls_protocols=\!SSLv2,\!SSLv3 \
+	smtpd_tls_protocols="!SSLv2,!SSLv3,!TLSv1,!TLSv1.1" \
-	smtpd_tls_ciphers=medium \
+	smtpd_tls_mandatory_protocols="!SSLv2,!SSLv3,!TLSv1,!TLSv1.1" \
-	smtpd_tls_exclude_ciphers=aNULL,RC4 \
+	smtpd_tls_ciphers=high \
+	smtpd_tls_mandatory_ciphers=high \
+	smtpd_tls_exclude_ciphers= \
+	tls_high_cipherlist=ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384 \
+	tls_preempt_cipherlist=no \
 	smtpd_tls_received_header=yes
 
 # Prevent non-authenticated users from sending mail that requires being
@@ -143,8 +147,12 @@ tools/editconf.py /etc/postfix/main.cf \
 # offers it, otherwise it will transmit the message in the clear. Postfix will
 # accept whatever SSL certificate the remote end provides. Opportunistic TLS
 # protects against passive easvesdropping (but not man-in-the-middle attacks).
+# Since we'd rather have poor encryption than none at all, we use Mozilla's
+# "Old" recommendations at https://ssl-config.mozilla.org/#server=postfix&server-version=3.3.0&config=old&openssl-version=1.1.1
+# for opportunistic encryption but "Intermediate" recommendations when DANE
+# is used (see next and above).
+
 # DANE takes this a step further:
-#
 # Postfix queries DNS for the TLSA record on the destination MX host. If no TLSA records are found,
 # then opportunistic TLS is used. Otherwise the server certificate must match the TLSA records
 # or else the mail bounces. TLSA also requires DNSSEC on the MX host. Postfix doesn't do DNSSEC
@@ -157,11 +165,13 @@ tools/editconf.py /etc/postfix/main.cf \
 # now see notices about trusted certs. The CA file is provided by the package `ca-certificates`.
 tools/editconf.py /etc/postfix/main.cf \
 	smtp_tls_protocols=\!SSLv2,\!SSLv3 \
-	smtp_tls_mandatory_protocols=\!SSLv2,\!SSLv3 \
 	smtp_tls_ciphers=medium \
-	smtp_tls_exclude_ciphers=aNULL,RC4 \
+	tls_medium_cipherlist=ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA256:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA \
+	smtp_tls_exclude_ciphers= \
 	smtp_tls_security_level=dane \
 	smtp_dns_support_level=dnssec \
+	smtp_tls_mandatory_protocols="!SSLv2,!SSLv3,!TLSv1,!TLSv1.1" \
+	smtp_tls_mandatory_ciphers=high \
 	smtp_tls_CAfile=/etc/ssl/certs/ca-certificates.crt \
 	smtp_tls_loglevel=2
 

setup/web.sh

@@ -31,14 +31,19 @@ sed "s#STORAGE_ROOT#$STORAGE_ROOT#" \
 	conf/nginx-ssl.conf > /etc/nginx/conf.d/ssl.conf
 
 # Fix some nginx defaults.
+#
 # The server_names_hash_bucket_size seems to prevent long domain names!
 # The default, according to nginx's docs, depends on "the size of the
 # processor’s cache line." It could be as low as 32. We fixed it at
 # 64 in 2014 to accommodate a long domain name (20 characters?). But
 # even at 64, a 58-character domain name won't work (#93), so now
 # we're going up to 128.
+#
+# Drop TLSv1.0, TLSv1.1, following the Mozilla "Intermediate" recommendations
+# at https://ssl-config.mozilla.org/#server=nginx&server-version=1.17.0&config=intermediate&openssl-version=1.1.1.
 tools/editconf.py /etc/nginx/nginx.conf -s \
-	server_names_hash_bucket_size="128;"
+	server_names_hash_bucket_size="128;" \
+	ssl_protocols="TLSv1.2 TLSv1.3;"
 
 # Tell PHP not to expose its version number in the X-Powered-By header.
 tools/editconf.py /etc/php/7.2/fpm/php.ini -c ';' \