On Tue, 26 May 2020, mj wrote:
On 25/05/2020 23:04, Voytek wrote:
jumping here with a question, if I use 143 with STARTTLS, and, force TLS/SSL in configuration, that's equivalent from security POV, isn't it? and, same for 110 STARTTLS? Or am I missing something?
There's an important clause here that often becomes overlooked: "force TLS/SSL in [client] configuration". If you don't fulfil this condition, STARTTLS can fall prey to downgrade attacks. This has been done, and not by small players:
https://www.eff.org/deeplinks/2014/11/starttls-downgrade-attacksSome mail readers, like macOX Mail, will happily reconfigure your mail reader server settings to use plaintext unless you disable it.
Interesting point, after some googling, I think you are right, and as long as we have set "disable_plaintext_auth = yes" (and we have that) we should be fine keeping 143 open. Right?
Yes, provided the above condition is met. However, unless you control all endpoints, that's hard to enforce.
One doubt I had: "disable_plaintext_auth = yes" sounds as if only the authentication part is secured, and the rest is kept plain text, whereas with 993/SSL, *everything* would be encrypted?
Once STARTTLS negotiations are over, it is equivalent to SSL: all data is encrypted. However, I see your point: the configuration label suggests it's limited to authentication data, as opposed to all data. Something like "ssl_forbid_decline" or "ssl_not_optional" might have been clearer.
Joseph Tam jtam.home@gmail.com