Re: [qmailtoaster] SSL Problem Dovecot

[Andrew Swartz]

Some background:

During the TLS negotiation, the client gives the server a list of 
ciphers which it supports, then from that list the server chooses which 
one to use.


The server's cipher list is a list, in order of preference, of the 
ciphers it will use (from the client's list).  If there is no overlap 
between what the client offers and what the server requires, then the 
connection fails.


The server dose not use the cipher list itself, but rather just passes 
the list to openssl when it requests establishment of the TLS 
connection.  Therefore essentially all servers/clients use the same 
format cipherlist.


The next thing to know is that the list can specify individual ciphers 
or macros like "TLSv1.2".  Most people do not specify individual ciphers 
but rather just use the macros.


There is no right or wrong for a cipher list, as the most appropriate 
list is the one which best meets your security requirements.


The cipherlist "builds" a list of ciphers:

'ALL' adds all of the ciphers (including those with no encrpytion).

'ALL:-SSLv2' adds all the ciphers and then removes all of the SSLv2 ciphers.

A reasonable cipherlist is:
'HIGH:-SSLv3'

If you want "perfect forward secrecy", try this:
'ECDHE:DHE:-SSLv3'
This will yield a subset of the TLSv1.2 ciphers which has the 
elliptic-curve diffie-hellman-ephemerel ciphers first and then standard 
diffie-hellman-ephemerel ciphers after that.


If you put that into openssl ciphers ( openssl ciphers -v 'HIGH:-SSLv3') 
you will note that you only get TLSv1.2 ciphers.  That is because an 
important concept is the difference between ciphers and protocols.  TLS 
1.0 and 1.1 updated the protocol but added no new ciphers.  (you can 
confirm this by comparing "openssl ciphers -v 'SSLv3' | md5sum" to 
"openssl ciphers -v 'TLSv1' | md5sum"; you'll get an error if you do it 
with TLSv1.1 because it does not even have a list of ciphers).


But note that older servers, such as centos 5, will not be able to 
connect to you (if you use 'ECDHE:DHE:-SSLv3') because their old version 
of openssl does not support TLSv1.2.  In that case, for STARTTLS, it 
will fail, which will default to smtp transmission as cleartext.  SMTP 
is somewhat forgiving, as a failed STARTTLS connection will fall back to 
cleartext, whereas most other TLS protocols will fail to connect.


This is a segway into the related topic of "protocols".  Many servers 
(like dovecot) have separate a setting for "TLS cipherlist" and "TLS 
protocol".  The protocol is the algorithm for establishing the 
connection, and it is independent of the ciphers.  You should avoid the 
SSLv3 or TLSv1 protocols, as the these protocols have been found to have 
weaknesses in how they negotiate the connection (completely unrelated to 
the strength of the ciphers).


This manpage is a good explanation of all the macros and has examples at 
the end:

https://www.openssl.org/docs/man1.0.2/man1/ciphers.html

People with older versions of openssl (i.e. Centos 5) cannot do TLSv1.2 
and will have no choice but to use ciphers/protocols with known 
weaknesses, and then hope that the other servers do not try to force a 
certain level of cipher/protocol.  That is not supposed to happen (per 
smtp/STARTTLS protocol), but I know for a fact that does:  I finally 
decided to upgrade from centos-5 because an important mail server 
started refusing to receive mail from mine, with a complaint about not 
accepting the SSLv3 ciphers.  I think it was Outlook Server, but I'm not 
sure.


Hope this helps.

-Andy

PS: Someone running the old version of openssl will need to put '-SSLv2" 
at the end of the cipherlist, whereas the newer version no longer 
supports it so it doesn't require removing it.  And NO ONE should be 
using the SSLv2 protocol, as hacking it is trivial.








On 9/3/2019 1:22 PM, CarlC Internet Services Service Desk wrote:
Actually, doing the openssl ciphers > /var/qmail/control/tlsservercipher 
is a starting point.


After I did that, I then ran my server through some tests. I happen to 
use OpenVAS [which tool you want to use to find insecure SSL connections 
is up to you]. It was able to tell me which ciphers to disable and why. 
Whichever product you use to test the SSL should be one that’s up to 
date [or can be brought up to date]. For example, I run the tests 
against my email server every week [for example, I test against port 25, 
465 and 587]. In my case, I also use OpenVAS to test the HTTPS side as well.


If you’re using dovecot, you will want to also put the ssl_cipher_list 
in /etc/dovecot/dovecot.conf as well as the ssl_protocols list. This 
protects your IMAPS and POP3S protocols. Again, OpenVAS is set to run 
against those protocols as well.


Carl

*From:*Gary Bowling [mailto:g...@gbco.us]
*Sent:* Tuesday, September 03, 2019 03:35 PM
*To:* qmailtoaster-list@qmailtoaster.com
*Subject:* Re: [qmailtoaster] SSL Problem Dovecot

Thanks for that Carl. I'm running openssl-1.0.2k-16.el7_6.1.x86_64

Pretty much 

RE: [qmailtoaster] SSL Problem Dovecot

[CarlC Internet Services Service Desk]

Actually, doing the openssl ciphers > /var/qmail/control/tlsservercipher is a 
starting point.

 

After I did that, I then ran my server through some tests. I happen to use 
OpenVAS [which tool you want to use to find insecure SSL connections is up to 
you]. It was able to tell me which ciphers to disable and why. Whichever 
product you use to test the SSL should be one that’s up to date [or can be 
brought up to date]. For example, I run the tests against my email server every 
week [for example, I test against port 25, 465 and 587]. In my case, I also use 
OpenVAS to test the HTTPS side as well.

 

If you’re using dovecot, you will want to also put the ssl_cipher_list in 
/etc/dovecot/dovecot.conf as well as the ssl_protocols list. This protects your 
IMAPS and POP3S protocols. Again, OpenVAS is set to run against those protocols 
as well.

 

Carl

 

From: Gary Bowling [mailto:g...@gbco.us] 
Sent: Tuesday, September 03, 2019 03:35 PM
To: qmailtoaster-list@qmailtoaster.com
Subject: Re: [qmailtoaster] SSL Problem Dovecot

 

 

Thanks for that Carl. I'm running openssl-1.0.2k-16.el7_6.1.x86_64

 

Pretty much everything about my server is continuously updated stock Centos 7. 
Currently at CentOS Linux release 7.6.1810 (Core)

 

I do have epel installed, which updates some things and the qmt repo. That's 
it, and I'm a stickler for NOT installing anything that isn't done through yum 
and those repos. I've done this long enough to know that it's much easier to 
maintain, migrate to a new server, etc. is you're running everything in a 
managed way. So installing the repos and doing yum installs is pretty much the 
only way anything ever changes on my server, sans config files.

 

Would be very interested in knowing not only the proper tlsservercipher file 
for this type of server, but also how to create/recreate it if it's a command 
done from openssl. Looks like you can create it with the command.

 

openssl ciphers > /var/qmail/control/tlsservercipher

 

But what I'm reading is that your advice is to NOT do that due to security 
concerns. So what would you recommend?

 

Thanks, Gary

 

On 9/3/2019 3:28 PM, CarlC Internet Services Service Desk wrote:

Your real problem is that this file is different based on which CentOS you’re 
on [or should I say, which openssl is loaded]. If you have CentOS 7, with 
openssl 1.0.2k, you can tune this file to include each cipher you want [the 
file can actually be 10+ lines long wrapped]. This is so you can remove all the 
“hacked” ciphers, especially to force your clients security to remain high. If 
your running openssl 0.9.x, you don’t get the newer TLS ciphers you need to be 
secure.

 

Using the default is way too low, and if you do, you will where someone gets 
hacked over a ‘free’ WiFi connection [because you had SSL 3.0/TLS 1.0 on].

 

Carl

 

From: Gary Bowling [mailto:g...@gbco.us] 
Sent: Tuesday, September 03, 2019 02:58 PM
To: qmailtoaster-list@qmailtoaster.com 
 
Subject: Re: [qmailtoaster] SSL Problem Dovecot

 

 

So this may be an issue of the tlsserverciphers file. Some times it's 
interesting not knowing what your doing! haha

 

I guess the question I have is.. What is the proper tlsserverciphers for a 
qmailtoaster with a letsencrypt certificate. If that even makes sense.

 

And what is the proper way to actually do it. I've read multiple things on 
various forums, including here. 

 

One says to do:

echo 
"!EDH:!DHE:!RC4:!ADH:!DSS:HIGH:+AES128:+AES256-SHA256:+AES128-SHA256:+SHA:!3DES:!NULL:!aNULL:!eNULL"
 > /var/qmail/control/tlsserverciphers

 

One says to do:

openssl ciphers 'MEDIUM:HIGH:!SSLv2:!MD5:!RC4:!3DES' > 
/var/qmail/control/tlsserverciphers

 

yet another says to create a sym link to the servercert.pem file. 

 

ln -sf /var/qmail/control/servercert.pem /var/qmail/control/tlsserverciphers

 

 

I guess it has to do with how tight you want security to be and maybe 
tlsserverciphers can contain various forms of how to define that. Just looking 
for what "most" people would use for an up to date Centos 7 server.

 

Thanks, Gary

 

On 9/3/2019 11:04 AM, Gary Bowling wrote:

 

I had to get a new cert for my server, which I installed yesterday. Now I'm 
having problems with certain clients logging in. I get the following error in 
the dovecot.log.

 

TLS handshaking: SSL_accept() failed: error:1408A10B:SSL routines: 
ssl3_get_client_hello:wrong version number

 

Any help would be appreciated. 

 

Thanks, Gary 

-- 

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Re: [qmailtoaster] SSL Problem Dovecot

[Gary Bowling]

  
  


Thanks for that Carl. I'm running
  openssl-1.0.2k-16.el7_6.1.x86_64


Pretty much everything about my server is continuously updated
  stock Centos 7. Currently at CentOS Linux release 7.6.1810 (Core)


I do have epel installed, which updates some things and the qmt
  repo. That's it, and I'm a stickler for NOT installing anything
  that isn't done through yum and those repos. I've done this long
  enough to know that it's much easier to maintain, migrate to a new
  server, etc. is you're running everything in a managed way. So
  installing the repos and doing yum installs is pretty much the
  only way anything ever changes on my server, sans config files.


Would be very interested in knowing not only the proper
  tlsservercipher file for this type of server, but also how to
  create/recreate it if it's a command done from openssl. Looks like
  you can create it with the command.



openssl ciphers > /var/qmail/control/tlsservercipher


But what I'm reading is that your advice is to NOT do that due to
  security concerns. So what would you recommend?



Thanks, Gary



On 9/3/2019 3:28 PM, CarlC Internet
  Services Service Desk wrote:


  
  
  
  
Your
real problem is that this file is different based on which
CentOS you’re on [or should I say, which openssl is loaded].
If you have CentOS 7, with openssl 1.0.2k, you can tune this
file to include each cipher you want [the file can actually
be 10+ lines long wrapped]. This is so you can remove all
the “hacked” ciphers, especially to force your clients
security to remain high. If your running openssl 0.9.x, you
don’t get the newer TLS ciphers you need to be secure.
 
Using
the default is way too low, and if you do, you will where
someone gets hacked over a ‘free’ WiFi connection [because
you had SSL 3.0/TLS 1.0 on].
 
Carl
 

  
From:
Gary Bowling [mailto:g...@gbco.us] 
Sent: Tuesday, September 03, 2019 02:58 PM
To: qmailtoaster-list@qmailtoaster.com
Subject: Re: [qmailtoaster] SSL Problem Dovecot
  

 
 
So this may be an issue of the tlsserverciphers file. Some
  times it's interesting not knowing what your doing! haha
 
I guess the question I have is.. What is the proper
  tlsserverciphers for a qmailtoaster with a letsencrypt
  certificate. If that even makes sense.
 
And what is the proper way to actually do it. I've read
  multiple things on various forums, including here. 
 
One says to do:
echo
"!EDH:!DHE:!RC4:!ADH:!DSS:HIGH:+AES128:+AES256-SHA256:+AES128-SHA256:+SHA:!3DES:!NULL:!aNULL:!eNULL"
  > /var/qmail/control/tlsserverciphers
 
One says to do:
openssl ciphers 'MEDIUM:HIGH:!SSLv2:!MD5:!RC4:!3DES' >
  /var/qmail/control/tlsserverciphers
 
yet another says to create a sym link to the servercert.pem
  file. 
 
ln -sf /var/qmail/control/servercert.pem
  /var/qmail/control/tlsserverciphers
 
 
I guess it has to do with how tight you want security to be
  and maybe tlsserverciphers can contain various forms of how to
  define that. Just looking for what "most" people would use for
  an up to date Centos 7 server.
 
Thanks, Gary
 

  On 9/3/2019 11:04 AM, Gary Bowling wrote:


   
  I had to get a new cert for my server, which I installed
yesterday. Now I'm having problems with certain clients
logging in. I get the following error in the dovecot.log.
   
  TLS handshaking: SSL_accept() failed: error:1408A10B:SSL
routines: ssl3_get_client_hello:wrong version number
   
  Any help would be appreciated. 
   
  Thanks, Gary 
  
-- 
  
  Gary Bowling
  
  
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RE: [qmailtoaster] SSL Problem Dovecot

[CarlC Internet Services Service Desk]

Your real problem is that this file is different based on which CentOS you’re 
on [or should I say, which openssl is loaded]. If you have CentOS 7, with 
openssl 1.0.2k, you can tune this file to include each cipher you want [the 
file can actually be 10+ lines long wrapped]. This is so you can remove all the 
“hacked” ciphers, especially to force your clients security to remain high. If 
your running openssl 0.9.x, you don’t get the newer TLS ciphers you need to be 
secure.

 

Using the default is way too low, and if you do, you will where someone gets 
hacked over a ‘free’ WiFi connection [because you had SSL 3.0/TLS 1.0 on].

 

Carl

 

From: Gary Bowling [mailto:g...@gbco.us] 
Sent: Tuesday, September 03, 2019 02:58 PM
To: qmailtoaster-list@qmailtoaster.com
Subject: Re: [qmailtoaster] SSL Problem Dovecot

 

 

So this may be an issue of the tlsserverciphers file. Some times it's 
interesting not knowing what your doing! haha

 

I guess the question I have is.. What is the proper tlsserverciphers for a 
qmailtoaster with a letsencrypt certificate. If that even makes sense.

 

And what is the proper way to actually do it. I've read multiple things on 
various forums, including here. 

 

One says to do:

echo 
"!EDH:!DHE:!RC4:!ADH:!DSS:HIGH:+AES128:+AES256-SHA256:+AES128-SHA256:+SHA:!3DES:!NULL:!aNULL:!eNULL"
 > /var/qmail/control/tlsserverciphers

 

One says to do:

openssl ciphers 'MEDIUM:HIGH:!SSLv2:!MD5:!RC4:!3DES' > 
/var/qmail/control/tlsserverciphers

 

yet another says to create a sym link to the servercert.pem file. 

 

ln -sf /var/qmail/control/servercert.pem /var/qmail/control/tlsserverciphers

 

 

I guess it has to do with how tight you want security to be and maybe 
tlsserverciphers can contain various forms of how to define that. Just looking 
for what "most" people would use for an up to date Centos 7 server.

 

Thanks, Gary

 

On 9/3/2019 11:04 AM, Gary Bowling wrote:

 

I had to get a new cert for my server, which I installed yesterday. Now I'm 
having problems with certain clients logging in. I get the following error in 
the dovecot.log.

 

TLS handshaking: SSL_accept() failed: error:1408A10B:SSL routines: 
ssl3_get_client_hello:wrong version number

 

Any help would be appreciated. 

 

Thanks, Gary 

-- 

Gary Bowling


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Re: [qmailtoaster] SSL Problem Dovecot

[Gary Bowling]

  
  


So this may be an issue of the tlsserverciphers file. Some times
  it's interesting not knowing what your doing! haha



I guess the question I have is.. What is the proper
  tlsserverciphers for a qmailtoaster with a letsencrypt
  certificate. If that even makes sense.



And what is the proper way to actually do it. I've read multiple
  things on various forums, including here. 



One says to do:
 echo
"!EDH:!DHE:!RC4:!ADH:!DSS:HIGH:+AES128:+AES256-SHA256:+AES128-SHA256:+SHA:!3DES:!NULL:!aNULL:!eNULL"
  > /var/qmail/control/tlsserverciphers


One says to do:
openssl ciphers 'MEDIUM:HIGH:!SSLv2:!MD5:!RC4:!3DES' >
  /var/qmail/control/tlsserverciphers


yet another says to create a sym link to the servercert.pem file.
  



ln -sf /var/qmail/control/servercert.pem
  /var/qmail/control/tlsserverciphers




I guess it has to do with how tight you want security to be and
  maybe tlsserverciphers can contain various forms of how to define
  that. Just looking for what "most" people would use for an up to
  date Centos 7 server.



Thanks, Gary



On 9/3/2019 11:04 AM, Gary Bowling
  wrote:


  
  
  
  I had to get a new cert for my server, which I installed
yesterday. Now I'm having problems with certain clients logging
in. I get the following error in the dovecot.log.
  
  
  TLS handshaking: SSL_accept() failed: error:1408A10B:SSL
routines: ssl3_get_client_hello:wrong version number
  
  
  Any help would be appreciated. 
  
  
  
  Thanks, Gary 
  
  -- 

Gary Bowling

  
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[qmailtoaster] SSL Problem Dovecot

[Gary Bowling]

  
  


I had to get a new cert for my server, which I installed
  yesterday. Now I'm having problems with certain clients logging
  in. I get the following error in the dovecot.log.


TLS handshaking: SSL_accept() failed: error:1408A10B:SSL
  routines: ssl3_get_client_hello:wrong version number


Any help would be appreciated. 



Thanks, Gary 

-- 
  
  Gary Bowling
  

  


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