Securing and optimizing SSL / SSL Tweaking

Securing and optimizing SSL / SSL Tweaking

SSL tweaks

If you configure a web server’s TLS configuration, you have primarily to take care of the following things.

Configuring HTTPS servers

SSL Session Cache

Enable session cache:

ssl_session_cache shared:SSL:20m;
ssl_session_timeout 10m;

ssl_session_cache in ngx_http_ssl_module

Use only secure protocols

Use only secure protocols:

  • disable SSL 2.0 (FUBAR) and SSL 3.01 (POODLE)
  • disable TLS 1.0 compression (CRIME)

Nginx Disabling SSL v3

The SSL Cipher Suite

We need to choosing both secure and fast SSL Ciphers. The bible, specially on ciphers is this article - Hardening Your Web Server’s SSL Ciphers

Choose chipers:

  • disable weak ciphers (DES, RC4)
  • and prefer modern ciphers (AES), modes (GCM) and protocols (TLS 1.2).

On nginx, configuration will look like this:

ssl_prefer_server_ciphers on;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:!aNULL:!MD5:!DSS;

The cipher list is kind of long, but it will work on most older browsers, if you don’t need to think about IE 8 then you can use this short one:

# This was default on nginx
ssl_ciphers HIGH:!aNULL:!MD5;

Sources

Security/Server Side TLS Enable Perfect Forward Secrecy for nginx

OCSP Stapling

It means that you sent status info about your certificate along with the request, instead of making the browser check the certificate with the Certificate Authority. This removes a large portion of the SSL overhead.

OCSP Stapling: How CloudFlare Just Made SSL 30% Faster

In nginx, it’s should be easy. The following config uses Google’s DNS for resolving and assumes your certificate file contains the entire certificate chain.

# OCSP stapling
#
ssl_stapling on;
ssl_stapling_verify on;
#
# Using Google DNS & OpenDNS
resolver 8.8.8.8 8.8.4.4 208.67.222.222 208.67.220.220 valid=60s;
resolver_timeout 2s;

If intermediate certificate is not already in ssl_certificate, we must add a ssl_trusted_certificate directive with file made up of your intermediate certificate followed by root certificate.

PositiveSSL Setup on Nginx

Testing if it’s working:

echo QUIT | openssl s_client -connect hostingtipp.ch:443 -servername hostingtipp.ch -status 2> /dev/null | grep -A 17 'OCSP response:' | grep -B 17 'Next Update'

Note that we need to use OpenSSL’s s_client directive for web servers using Server Name Indication (SNI).

Important note

OCSP won’t be detected on first request. Simply put, nginx needs some time to fetch the OCSP response and cache it for all clients. After running the above OpenSSL command several times the test would show up successful. Additionally, the first request to a worker will never have an OCSP response stapled.

Sources

OCSP Stapling in Nginx OCSP Stapling on nginx How To Configure OCSP Stapling on Apache and Nginx Can’t get OCSP stapling to work

ssl_stapling in ngx_http_ssl_module

HTTP Strict Transport Security (HSTS)

HTTP Strict Transport Security (HSTS) will force the browser to load all subsequent requests from the same host over https, even when you’ve linked to http. So we just need to add and enable Strict Transport Security header.

In nginx, you add this like this:

# force every request after this to be over HTTPS
add_header Strict-Transport-Security "max-age=31536000";
Sources & articles

SSL Security

Still not fixed a Clickjacking wich can be done by using X-Frame-Options.

POODLE attack

Fix POODLE exploit on every Plesk service including Parallels Plesk service, Apache, Postfix SMTP, Courier or Dovecot IMAP/POP3 server, ProFTPD server and of course nginx.

POODLE Scan POODLE SSL Vulnerability Check

How do I patchSSLv3 POODLE vulnerability?

BEAST attack

BEAST is purely a client-side vulnerability. BEAST has been mitigated by most browsers on the client side. The only major browser holding out has been Safari. Although I don’t believe that the problem is exploitable today

Security Labs: Is BEAST Still a Threat?

Sources & articles

Very good article overall about this: Strong SSL Security on nginx and also this one: Is TLS Fast Yet?

SSL Verification

There are some tools to check SSL configuration and validity. The most detailed security test is Qualys’s SSL Server Test. The same tool can be found on GlobalSign site, but with different UX.

SSL Certificate Checker GeoCerts SSL Checker Comodo SSL Analyzer

Plesk

If we already created our custom domain template:

nano /usr/local/psa/admin/conf/templates/custom/domain/nginxDomainVirtualHost.php
nano /usr/local/psa/admin/conf/templates/custom/server/nginxVhosts.php

# reconfigure domains
plesk sbin httpdmng --reconfigure-domain hostingtipp.ch

Plesk custom domain templates

Create a new custom domain templates. Maybe you have them already, for some other purpose.

mkdir -p /usr/local/psa/admin/conf/templates/custom/
mkdir -p /usr/local/psa/admin/conf/templates/custom/server/
mkdir -p /usr/local/psa/admin/conf/templates/custom/domain/

cp /usr/local/psa/admin/conf/templates/default/domain/nginxDomainVirtualHost.php /usr/local/psa/admin/conf/templates/custom/domain/
cp /usr/local/psa/admin/conf/templates/default/server/nginxVhosts.php /usr/local/psa/admin/conf/templates/custom/server/

Plesk custom domain templates

sed -i 's/ssl_protocols               SSLv2 SSLv3 TLSv1;/ssl_protocols               TLSv1 TLSv1.1 TLSv1.2;/g' /usr/local/psa/admin/conf/templates/custom/nginxWebmailPartial.php
sed -i 's/ssl_protocols               SSLv2 SSLv3 TLSv1;/ssl_protocols               TLSv1 TLSv1.1 TLSv1.2;/g' /usr/local/psa/admin/conf/templates/custom/domain/nginxDomainVirtualHost.php
sed -i 's/ssl_protocols               SSLv2 SSLv3 TLSv1;/ssl_protocols               TLSv1 TLSv1.1 TLSv1.2;/g' /usr/local/psa/admin/conf/templates/custom/server/nginxVhosts.php

Using Plesk internal variables

There is a better way for disabling SSLv3, by using Plesk variable disablesslv3.

How to set Plesk variable?

mysql -uadmin -p`cat /etc/psa/.psa.shadow` -Dpsa -e "insert into misc values('disablesslv3', 'true')"

# reconfigure domains
plesk sbin httpdmng --reconfigure-all

# and check
grep ssl_protocols /var/www/vhosts/system/*/conf/last_nginx.conf

When using this way, I try to minimize Sources:

To do


At the end, this is the great setting:

# Speed up SSL handshake
#
# OCSP stapling, Using Google DNS & OpenDNS
#
ssl_stapling on;
ssl_stapling_verify on;
resolver 8.8.8.8 8.8.4.4 208.67.222.222 208.67.220.220 valid=60s;
resolver_timeout 2s;
#
# SSL Session Cache
ssl_session_cache shared:SSL:20m;
ssl_session_timeout 10m;
#
# Use fastest ciphers: these shaved off 50ms
# SSL Negotiation should be ~80ms, down from ~130ms
ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!3DES:!MD5:!PSK;
date 01. Jan 0001 | modified 28. May 2021
filename: Server - SSL Tweaking