TLSv1.0, used not only for HTTPS but also for secure SMTP, IMAP, etc., has been around for a while — 1999, in fact –, and, while not “hopelessly broken” like SSL 2 and 3 are, there have been many successful attacks/exploits against it in the past two decades, and while most implementations (in terms of both servers and clients) have been patched to work around those, there may always be another one just around the corner. Also, TLSv1.0 came from a time where it was desirable to support as many different ciphers as possible, which means that, by default, some ciphers later found to be insecure may still be enabled.
Therefore, the end of TLSv1.0 has been talked about for a while, and, indeed, the main browser vendors — Google, Mozilla, Apple, and Microsoft — have announced that they’ll deprecate TLSv1.0 (and 1.1, which is little more than a revision of 1.0) by early 2020.
Now, until a few days ago I still had TLSv1.0 enabled on my servers (including Nginx, Postfix and Dovecot); my belief was that some encryption was always better than no encryption, and besides we were mostly talking about public websites, that didn’t ask for user credentials or anything. Furthermore, any modern browsers/email clients default to secure protocols (TLSv1.2 or better), so there would never be, “in real life”, a situation where important/sensitive data (say, me logging on to my own mail server, or to one of my WordPresses was being transmitted in an insecure way.
On the other hand… doesn’t the above mean that, “in real life”, nobody will really be using TLSv1.0 “legitimately”? Doesn’t it mean that setting up TLSv1.2 as a minimum will have no adverse consequences?
So I investigated it a little:
- in terms of browsers/clients, requiring TLSv1.2 or above means: 1) no Internet Explorer before version 11; 2) no Safari before 6.x; 3) no default Android browser before Android 4.4.x (but those users can still use Chrome or other non-default browsers). (You can check this out on SSL Labs). I don’t have a way to check email clients that old, but you can assume that anything released after the browsers just mentioned will be OK;
- in terms of my own server logs (mostly Nginx, but also Postfix, in terms of opportunistic encryption), apparently, only spambots and such are using TLSv1.0; any “legitimate” email servers use TLSv1.2 or 1.3. The same thing with my websites — any TLSv1.0 entries in my logs are always from some bot (and not one for a “well-known” search engine), not actual visitors. 1
In short: you can probably move to requiring TLSv1.2 or above now (and, indeed, I’ve done so since a few days ago), unless you’re in some very peculiar situation — maybe your site needs to be accessed by users of a company whose IT policy includes not using software newer than 20 years old? Or you have a CEO who’s always refused to upgrade his beloved Symbian phone, but who’d flip out if he couldn’t access your company’s webmail with it? 🙂 Otherwise, my advice is: go TLSv1.2 and don’t look back.
However, and since this post is already quite long, I’ll leave the specific instructions for disabling TLS before 1.2 in Nginx, Apache, Postfix, and Dovecot for the next one…