SSL Settings
SSL Settings
Further to some recent discussions on PCI-DSS compliance this is a guide to updating some of the security settings in SME Server.
Currently SSLv2, SSLv3 and TLSv1.0 should not be used.
SME Server can use TLS v1.2 and TLS v1.1 but due to the openssl version it cannot provide TLSv1.3
SSL/TLS
Disabling TLSv1.0 per service
HTTPS
Remove TLSv1.0 port 443
config setprop httpd-e-smith TLSv1 disabled expand-template /etc/httpd/conf/httpd.conf /etc/init.d/httpd-e-smith restart
IMAPS
Remove TLSv1.0 port 993 imaps (dovecot)
config setprop dovecot TLSv1 disabled signal-event email-update
SMTPS
Remove TLSv1.0 port 465
config setprop qpsmtpd TLSv1 disabled signal-event email-update
POP3S
POP3s is really a secure stunnel connection back to standard POP3
Remove TLSv1.0 port 995
config setprop pop3s TLSv1 disabled signal-event email-update
Ciphers
First we should add a template fragment for pop3s
mkdir -p /etc/e-smith/templates-custom/var/service/pop3s/stunnel.conf/ cp /etc/e-smith/templates/var/service/pop3s/stunnel.conf/10ssl /etc/e-smith/templates-custom/var/service/pop3s/stunnel.conf/ nano /etc/e-smith/templates-custom/var/service/pop3s/stunnel.conf/10ssl
Add these lines after "$OUT .= "options = NO_TLSv1\n" unless ($pop3s{TLSv1} || 'enabled') eq 'enabled';"
# Disable weak ciphers
$OUT .= "ciphers = " . ($pop3s{CipherSuite} || $modSSL{CipherSuite} || 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4') . "\n";
Save.
Now we can set an overall Cipher or per service.
Overall we can use (There is no separate setting for https)
config setprop modSSL CipherSuite 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4'
If we set modSSL overall we can then change the following per service:
config setprop ldap CipherSuite 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4' config setprop ldap qpsmtpd tlsCipher 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4' config setprop ldap pop3s CipherSuite 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4'
Expand all templates and restart:
signal-event post-upgrade;signal-event reboot
Other settings
Existing keys
For reference here are the existing keys in /etc/e-smith/templates
etc/dovecot/dovecot.conf/35ssl:12:$OUT .= "ssl_cipher_list = " . ($dovecot{CipherSuite} || $modSSL{CipherSuite} || 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4') . "\n";
etc/httpd/conf/httpd.conf/35SSL10SSLCipherSuite:4: $OUT .= $modSSL{CipherSuite} || 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4';
etc/openldap/slapd.conf/12tls:2:TLSCipherSuite { $ldap{CipherSuite} || $modSSL{CipherSuite} || 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4' }
var/service/qpsmtpd/config/tls_ciphers/10ciphers:3: return $qpsmtpd{tlsCipher} || $modSSL{CipherSuite} || 'HIGH:!SSLv2:!ADH:!aNULL:!MD5:!RC4';
Preferred Ciphers
When testing at ssllabs.com we can see that these are the only Ciphers it feels are secure but currently we do have a specific Cipher setting to restrict it to these:
TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 (0x9e) TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xc02f) TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f) TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0xc030)
Testing
Test with:
nmap -p <port> --script ssl-enum-ciphers youserver.com
e.g.
nmap -p 995 --script ssl-enum-ciphers youserver.com
Test with:
openssl s_client -connect youserver.com:<port> -tls1
e.g.
openssl s_client -connect youserver.com:465 -tls1
Confirm access to TLSv1.1:
openssl s_client -connect youserver.com:465 -tls1_1
Note: if your server supports the protocol, You will get:
Protocol : TLSvX Cipher : XXX
(You my need to CTL C out)
If your server does not support the protocol, you will get
Secure Renegotiation IS NOT supported