FREAK/Logjam, and SSL protocols to use

[Ron Leach]

List, good afternoon,

I was reading up on a TLS Diffie Hellman protocol weakness described here

https://weakdh.org/sysadmin.html

which is similar to the earlier FREAK attack, and can result in 
downgrade of cipher suites.

Part of the solution workaround that the researchers describe for 
Dovecot here

https://weakdh.org/sysadmin.html

includes altering DH parameters length to 2048, and re-specifying the 
allowable cipher suites - they give their suggestion.

But the researchers make no comment on the allowable protocols that, 
in Dovecot, are controlled in 10-ssl.conf in the stanza headed

# SSL protocols to use
#ssl_protocols = !SSLv2

I couldn't find any advice on up-to-date SSL/TLS protocol settings in 
the Dovecot wiki, either (I looked in
http://wiki2.dovecot.org/SSL/DovecotConfiguration ).

At the moment our installation is using only the default settings for 
allowed protocols; I'm not sure what those defaults might be, but our 
10-ssl.conf may only be disallowing SSLv2, if the 'example' entry is 
the default.  We're running 2.2.15, and are due to upgrade to 2.2.18 
shortly; quite possibly the defaults differ in a more recent release.

What SSL protocols do folk on the list recommend should be allowed in 
Dovecot these days?  (Actually, I mean which protocols really 'must' 
be disallowed?)

regards, Ron