You can get away with a lot for a personal server that wouldn't be acceptable
for a general purpose email server such as the need to move the fence. In my
case, I don't allow anything on the email server to be altered with a browser
interface. It is either ssh or nothing. Browsers get more complicated as time
goes on and security is inversely related to complexity. I use MUAs for all my
email. Less is more.
I totally get why 2FA is useful. But if you are practicing good security
hygiene, the advantage is less than you think. All my passwords are 20
characters randomly generated and unique for everything, not just email. So
there is no risk from password reuse. 2FA is really only useful if your
personal devices have been breached and the plain text passwords are exposed.
So to be totally effective the 2FA should come from a hardware device like a
Ubikey or similar.
What I have done is to use the 2FA with financial institutions. So I block the
hackers where it matters. I can't stop attempts at my accounts being spoofed,
but I can stop the hackers where is matters. Use DKIM and hope those getting
your email check it.
But if there was a friction free means of adding 2FA to email, I would do it.
But it would have to be in the MUA and be supported by postfix and dovecot.
The OTP code is done. I have played with FreeOTP and associated Linux program
to recognize the token. (Name escapes me.) You just need everyone to agree on
how to glue it all together.
Original Message
From: sebast...@sebbe.eu
Sent: July 15, 2021 11:26 AM
To: dovecot@dovecot.org
Reply-to: dovecot@dovecot.org
Subject: Sv: Sv: function for whitelisting IPs
Yeah the idea was to use roundcube or other web service to add kind of "auth
service" or "unlock service" where you can auth with 2FA to move the geofence
or permit additional IPs in geofence. For example, if you are travelling or
otherwise need to enable your account for a "outsider IP".
This could be a simple webpage asking for username and 2FA code, and all it
does it adds the IP to auth list. But could be a full roundcube or other
webmail solution too, to give more usefullness to the web login solution if you
don't have a imap/smtp client for now.
I don't use 587 myself, but instead, I have set so auth is only permitted on
port 25 for authorized IPs (auth_advertise_hosts in exim), thus the server will
refuse to allow outsiders to authenticate.
In combination with some other policies, my server is practically rock solid.
-----Ursprungligt meddelande-----
Från: dovecot-boun...@dovecot.org <dovecot-boun...@dovecot.org> För lists
Skickat: den 15 juli 2021 20:09
Till: 'Mailing List' <dovecot@dovecot.org>
Ämne: Re: Sv: function for whitelisting IPs
I run a personal email server. I can't emphasize enough how geofencing has
reduced the useless hacking on my email server. I only leave port 25 open to
the world. I use port 587.
I maintain a list of hosting companies that I block from using my web server
since they are just going to scrape anyway. I also keep that IP space off of my
email other than port 25.
Firewalls use memory but tend to be very light on the CPU other than when you
first start up the firewall. I assume they take the deny list and create a
table in RAM to efficiently block IPs. I have found that dynamic IP blocking
programs such as sshguard or fail2ban are a CPU burden since that table needs
to be refreshed as new IPs are added or removed so I have stopped using them.
Not that the programs themselves are CPU intensive, but they cause the firewall
to be CPU intensive. I am considering using sshguard again but with a very high
threshold to add an IP to the deny list.
Regarding attempts to add 2FA by using RoundCube or similar web based email, I
think those programs just increase the attack surface. When I used a hosting
service I was hacked by an unpatched exploit in RoundCube.
Original Message
From: sebast...@sebbe.eu
Sent: July 15, 2021 3:55 AM
To: dovecot@dovecot.org
Reply-to: dovecot@dovecot.org
Subject: Sv: function for whitelisting IPs
Most such functions would need to be custom.
You need to write a custom login script, which also accepts the user's IP as
input to a function, which then checks if password is right.
And then it returns that password is invalid if IP isn't approved.
Then you just need to write some custom functions in roundcube or similiar to
have the webmail insert the IP into a database.
Or just match it against a GeoIP database and save the latest country the
webmail was logged in from, and then SMTP/IMAP is only approved for that
country.
That reduces the attack surface greatly.
-----Ursprungligt meddelande-----
Från: dovecot-boun...@dovecot.org <dovecot-boun...@dovecot.org> För White,
Daniel E. (GSFC-770.0)[NICS]
Skickat: den 15 juli 2021 12:21
Till: Dovecot Mailing List <dovecot@dovecot.org>
Ämne: function for whitelisting IPs
Sebastian,
Do you have any examples of such a function and how/where it is used ?
-----Original Message-----
From: dovecot <dovecot-boun...@dovecot.org> on behalf of Sebastian
<sebast...@sebbe.eu>
Reply-To: Dovecot Mailing List <dovecot@dovecot.org>
Date: Thursday, July 15, 2021 at 01:19
To: 'Mailing List' <dovecot@dovecot.org>
Subject: [EXTERNAL] Sv: 2FA/MFA with IMAP & postfix/submission
Main problem is that not many clients do natively support multifactor.
Some clients, do popup a login dialog if the server rejects the password as
invalid, which can be used to create a "cheaty variant" of multifactor, but
some clients just popup an error dialog and tell the user to just correct
password in settings.
Some clients even go as long as requiring the user to delete the account
with wrong password and set up a new connection.
So no, it cannot be relied upon.
I have a better idea:
Have a function for whitelisting IPs, possible /24's or similiar, where a
login to roundcube or other webmail client (with 2FA) will add the IP onto a
whitelist for that account.
Or perhaps, just "set" the country of the account based on GeoIP.
When an account tries to login via IMAP or SMTP, you just check if IP
and/or GeoIP country is right, and reject the login as invalid if so not.
The only thing a client needs to do to get his IMAP or SMTP client to work
again if it stops working, is to login once via the web client.
-----Ursprungligt meddelande-----
Från: dovecot-boun...@dovecot.org <dovecot-boun...@dovecot.org> För Alex
Skickat: den 15 juli 2021 02:10
Till: dovecot@dovecot.org
Ämne: 2FA/MFA with IMAP & postfix/submission
Hi, I have a dovecot-2.3.13 system on fedora34 with a few hundred
IMAP4 accounts, as well as postfix users using submission. Clients are
using primarily Outlook on Windows and old squirrelmail.
Are there multi-factor options available?
If it is not available, do you have any recommendations on where I
should look to do this?
All of the links related to this topic appear to be very old, or
limited to Linux PAM users.
