Cipher Order Determined by Client

[sveeke]

The badgr-dev2.edubadges.nl server allows the SSL/TLS cipher to be chosen by the client instead of the server. This could result in a less-than-optimal encryption algorithm being chosen for the encryption of sensitive data.

[sveeke]

The badgr-dev2.edubadges.nl server allows the SSL/TLS cipher to be chosen by the client instead of the server. This could result in a less-than-optimal encryption algorithm being chosen for the encryption of sensitive data.

When a TLS connection is established, a handshaking, known as the TLS
Handshake Protocol occurs. Within this handshake, a client hello
(ClientHello) and a server hello (ServerHello) message are passed. First,
the client sends a list of the cipher suites that it supports, in order of
preference. Then the server replies with the cipher suite that it has
selected from the client's list.

When the Cipher order is determined by the client this could result in a
lower encryption of the website traffic than would be possible.

The testssl.sh (www.testssl.sh) was used to find the issue.

./testssl.sh badgr-dev2.edubadges.nl

 Has server cipher order?     nope (NOT ok)

impact:
When the cipher order is determined by the client an attacker could force
the use of a weaker cipher to a clients computer. This could result to the
decryption of the traffic between user and website.

recommendation:
Enable server side cipher preference. In nginx.conf:

ssl_prefer_server_ciphers on;

[sveeke]

I'll take this one for the new environment.