[Dovecot] Enabling security on POP3 and IMAP

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Richard Hobbs

3 Sep 2009 3 Sep '09

8:38 a.m.

Hello,

Currently, on our new test server, I am offering IMAP on 143 and POP3 on 110.

We would like to enable security on both of these protocols to attempt to eliminate the risk from an internal password-grabbing/content-grabbing attack.

I presume this would mean enabling SSL, and a more securure authentication, right? Or are plain text passwords just sent over the SSL, and therefore perfectly secure?

Also, what are the steps to enable security for these protocols on an already-configured server?

Is it possible to offer encrypted and non-encrypted services simultaneously, so people have a choice of whether they want security or not? I know that's a bit weird, but for testing it would be useful.

Finally, is there a way to monitor which users are connecting over the secure ports and which users are connecting over the non-secure ports?

Thanks in advance!

Richard.

-- Richard Hobbs (IT Specialist) Toshiba Research Europe Ltd. - Cambridge Research Laboratory Email: richard.hobbs@crl.toshiba.co.uk Web: http://www.toshiba-europe.com/research/ Tel: +44 1223 436999 Mobile: +44 7811 803377

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Patrick Nagel

3 Sep 3 Sep

9:04 a.m.

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1

Hi Richard,

On 2009-09-03 16:38, Richard Hobbs wrote:

...

Currently, on our new test server, I am offering IMAP on 143 and POP3 on 110.

We would like to enable security on both of these protocols to attempt to eliminate the risk from an internal password-grabbing/content-grabbing attack.

I presume this would mean enabling SSL, and a more securure authentication, right? Or are plain text passwords just sent over the SSL, and therefore perfectly secure?

Yes, plain text passwords are fine with SSL/TLS, since the connection gets secured before the password is sent.

...

Also, what are the steps to enable security for these protocols on an already-configured server?

Is it possible to offer encrypted and non-encrypted services simultaneously, so people have a choice of whether they want security or not? I know that's a bit weird, but for testing it would be useful.

No problem. Basically you just need to specify the certificate (ssl_cert_file) and the key (ssl_key_file) in the config, and add 'imaps' and 'pop3s' to 'protocols'.

...

Finally, is there a way to monitor which users are connecting over the secure ports and which users are connecting over the non-secure ports?

You can see it in the log.

Patrick.

STAR Software (Shanghai) Co., Ltd. http://www.star-group.net/ Phone: +86 (21) 3462 7688 x 826 Fax: +86 (21) 3462 7779

PGP key: E883A005 https://stshacom1.star-china.net/keys/patrick_nagel.asc Fingerprint: E09A D65E 855F B334 E5C3 5386 EF23 20FC E883 A005 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/

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Richard Hobbs

10 Sep 10 Sep

9:13 a.m.

Hello,

Replies inline...

Patrick Nagel wrote:

...

OK, I'll do that then, unless it's not commonly what's done for some reason...

...

Thanks for the advice - how do i generate ssl cert files and ssl key files? Also, various people access our mail server over IP, or various different hostnames - can all of those be built into the key/cert files so they aren't continually warned about hostname mismatches?

...

Excellent.

Thanks again, Richard.

Christian Schmidt

11 Sep 11 Sep

8:02 a.m.

Hello Richard,

Richard Hobbs, 10.09.2009 (d.m.y):

...

Thanks for the advice - how do i generate ssl cert files and ssl key files?

Just use OpenSSL. There's a short description of what to do on <http://www.apache-ssl.org> - or in any other OpenSSL Howto...

Gruss/Regards, Christian Schmidt

-- Having nothing, nothing can he lose. -- William Shakespeare, "Henry VI"

Richard Hobbs

24 Sep 24 Sep

3:39 p.m.

Hello,

Thanks again for your response...

However, upon closer inspection, it seems that both "/etc/ssl/certs/dovecot.pem" and "/etc/ssl/private/dovecot.pem" already exist!

I'm running Debian Lenny 5.0 btw - does anyone know if these keys were simply part of the dovecot package, or whether they have been generated during the installation process and are therefore unique?

If they are unique, then I don't need to generate my own, perhaps?

Thanks again, Richard.

Christian Schmidt wrote:

...

Josep L. Guallar-Esteve

3:59 p.m.

Hello Richard,

Maybe the included .pem files are bad (expire, pointing to wrong server name or whatnot)

I'd generate new .pem files.

dovecot documentation points to mkcert.sh script. With this script you can generate your own certificate, after filling in the OpenSSL config file used by mkcert.sh.

On my system, the script is located at /usr/libexec/dovecot/mkcert.sh

and the configuration file is at: /etc/pki/dovecot/dovecot-openssl.cnf

With the key and certificate generated this script, dovecot is happy to work with ssl (imaps i my case)

Hope this helps,

Josep

On Thursday 24 September 2009 11:39:59 am Richard Hobbs wrote:

...

-- Josep L. Guallar-Esteve - IT Department

This transmission is intended for the use of the entity or individual to which or whom it is addressed. The transmission or any documents accompanying the transmission may contain confidential information. If you are not the intended recipient, you are hereby notified that any disclosure, copying, distribution, or action taken in reliance on the contents of the transmission or the documents is strictly prohibited. If you have received this confidential transmission in error, please destroy it and any accompanying documents and notify the sender immediately. Thank you.

aja-lists

25 Sep 25 Sep

9:42 a.m.

Richard Hobbs wrote:

...

In Debian Lenny (and Etch) those keys are generated during the installation of the dovecot-imapd and/or dovecot-pop3d packages.

If you really want to re-do them, you can (re)move them, and then run apt-get install --reinstall dovecot-imapd dovecot-pop3d .

Richard Hobbs

28 Sep 28 Sep

10:01 a.m.

Hello,

...

Thanks for the advice... however, it has only partially worked.

When i "check what the server supports" in Kmail when setting up a new account in my email client, for POP3, it says it supports None, SSL and TLS and defaults to TLS, and auth methods are Clear text and Plain.

Is there a way to get rid of the "None" method for encryption? I do not have "pop3" in the protocols line - only "pop3s".

As for IMAP, the problem is worse... all i get for IMAP is "No encryption with clear text passwords". SSL/TLS just doesn't seem to be an option for IMAP despite "imaps" being in the protocols line and "imap" *not* being there.

For both these tests, rightly or wrongly, i used the standard ports (110 for POP3, 143 for IMAP). I know SSL typically operates on higher ports numbers, at least for IMAP, but I dont' know how this all works when you turn off non-encrypted protocols.

Any advice gratefully received!

Thanks again, Richard.

Patrick Nagel wrote:

...

This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email

Richard Hobbs

10:04 a.m.

Hello,

Sorry people - my problem is actually the opposite of what I wrote below... POP3 gives no encryption options whatsoever, and IMAP defaults correctly, but still gives the option for no encryption.

Also, the SSL section of dovecot.conf is here: http://pastebin.ca/1582348

Thanks again!

Richard.

Richard Hobbs wrote:

...

Hello,

...
...
Is it possible to offer encrypted and non-encrypted services simultaneously, so people have a choice of whether they want security or not? I know that's a bit weird, but for testing it would be useful. No problem. Basically you just need to specify the certificate (ssl_cert_file) and the key (ssl_key_file) in the config, and add 'imaps' and 'pop3s' to 'protocols'.

Thanks for the advice... however, it has only partially worked.

When i "check what the server supports" in Kmail when setting up a new account in my email client, for POP3, it says it supports None, SSL and TLS and defaults to TLS, and auth methods are Clear text and Plain.

Is there a way to get rid of the "None" method for encryption? I do not have "pop3" in the protocols line - only "pop3s".

As for IMAP, the problem is worse... all i get for IMAP is "No encryption with clear text passwords". SSL/TLS just doesn't seem to be an option for IMAP despite "imaps" being in the protocols line and "imap" *not* being there.

For both these tests, rightly or wrongly, i used the standard ports (110 for POP3, 143 for IMAP). I know SSL typically operates on higher ports numbers, at least for IMAP, but I dont' know how this all works when you turn off non-encrypted protocols.

Any advice gratefully received!

Thanks again, Richard.

Patrick Nagel wrote:

...
Hi Richard,

On 2009-09-03 16:38, Richard Hobbs wrote:

...
Currently, on our new test server, I am offering IMAP on 143 and POP3 on 110. We would like to enable security on both of these protocols to attempt to eliminate the risk from an internal password-grabbing/content-grabbing attack. I presume this would mean enabling SSL, and a more securure authentication, right? Or are plain text passwords just sent over the SSL, and therefore perfectly secure? Yes, plain text passwords are fine with SSL/TLS, since the connection gets secured before the password is sent.

...
Also, what are the steps to enable security for these protocols on an already-configured server? Is it possible to offer encrypted and non-encrypted services simultaneously, so people have a choice of whether they want security or not? I know that's a bit weird, but for testing it would be useful. No problem. Basically you just need to specify the certificate (ssl_cert_file) and the key (ssl_key_file) in the config, and add 'imaps' and 'pop3s' to 'protocols'.

...
Finally, is there a way to monitor which users are connecting over the secure ports and which users are connecting over the non-secure ports? You can see it in the log.

Patrick.

This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email

Richard Hobbs

10:13 a.m.

Hello,

Sorry people - i'm an idiot! ;-)

I was testing against our new hostnames that we setup for the new mail server. Trouble was - these hostnames were setup initially to point at the old mail server and are still doing so.

Having tested against the new mail server's IP address, everything works fine!

One question though... before I accept the certificate, i get warnings. One says the cert is not trusted (which is fine - it's self-signed). The other warning, however, mentions a hostname mismatch. Is there any way to put all of the hostnames we'll ever use into that certificate, so regardless of whether people are access "mail.domain", "pop3.domain" or "imap.domain", the hostname mismatch does not occur?

Thanks again!

Richard.

Richard Hobbs wrote:

...

Hello,

Sorry people - my problem is actually the opposite of what I wrote below... POP3 gives no encryption options whatsoever, and IMAP defaults correctly, but still gives the option for no encryption.

Also, the SSL section of dovecot.conf is here: http://pastebin.ca/1582348

Thanks again!

Richard.

Richard Hobbs wrote:

...
Hello,

...
...
Is it possible to offer encrypted and non-encrypted services simultaneously, so people have a choice of whether they want security or not? I know that's a bit weird, but for testing it would be useful. No problem. Basically you just need to specify the certificate (ssl_cert_file) and the key (ssl_key_file) in the config, and add 'imaps' and 'pop3s' to 'protocols'. Thanks for the advice... however, it has only partially worked.

When i "check what the server supports" in Kmail when setting up a new account in my email client, for POP3, it says it supports None, SSL and TLS and defaults to TLS, and auth methods are Clear text and Plain.

Is there a way to get rid of the "None" method for encryption? I do not have "pop3" in the protocols line - only "pop3s".

As for IMAP, the problem is worse... all i get for IMAP is "No encryption with clear text passwords". SSL/TLS just doesn't seem to be an option for IMAP despite "imaps" being in the protocols line and "imap" *not* being there.

For both these tests, rightly or wrongly, i used the standard ports (110 for POP3, 143 for IMAP). I know SSL typically operates on higher ports numbers, at least for IMAP, but I dont' know how this all works when you turn off non-encrypted protocols.

Any advice gratefully received!

Thanks again, Richard.

Patrick Nagel wrote:

...
Hi Richard,

On 2009-09-03 16:38, Richard Hobbs wrote:

...
Currently, on our new test server, I am offering IMAP on 143 and POP3 on 110. We would like to enable security on both of these protocols to attempt to eliminate the risk from an internal password-grabbing/content-grabbing attack. I presume this would mean enabling SSL, and a more securure authentication, right? Or are plain text passwords just sent over the SSL, and therefore perfectly secure? Yes, plain text passwords are fine with SSL/TLS, since the connection gets secured before the password is sent.

...
Also, what are the steps to enable security for these protocols on an already-configured server? Is it possible to offer encrypted and non-encrypted services simultaneously, so people have a choice of whether they want security or not? I know that's a bit weird, but for testing it would be useful. No problem. Basically you just need to specify the certificate (ssl_cert_file) and the key (ssl_key_file) in the config, and add 'imaps' and 'pop3s' to 'protocols'.

...
Finally, is there a way to monitor which users are connecting over the secure ports and which users are connecting over the non-secure ports? You can see it in the log.

Patrick.

This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email

Charles Marcus

10:59 a.m.

On 9/28/2009, Richard Hobbs (richard.hobbs@crl.toshiba.co.uk) wrote:

...

There is a way to add 'alternate names', but I don't think TBird (or most other Clients) will recognize them. You could also create a wildcard self-signed cert, but I think TBird will still give that error...

Of course, for TBird, you could install the 'remember mismatched domains' extension so you can make that 'error' go away...

Best regards,

Charles

Ed W

4:27 p.m.

Charles Marcus wrote:

...

Actually, I find them fully supported on all the clients I tried! (Not that many to be fair)

I am using a godaddy cert with multiple names and it's working just find and dandy with Thunderbird and Apple Mail for example. I believe others have reported success with various microsoft PDA's also (which is encouraging)

Godaddy simply had the cheapest cert when I was looking around, but you still pay many $10s for a cert with 5 or so extra aliases

Wildcard certs may also work for you if you are *.domain, but in my case I needed various domain1.com domain2.com type options

Good luck

Ed W

Edgar Fuß

4:41 p.m.

New subject: [Dovecot] Subject Alternativee Names (was: Enabling security on POP3 and IMAP)

...

There is a way to add 'alternate names' Subject Altenative Names.

...

but I don't think TBird (or most other Clients) will recognize them. The only client I know of NOT suporting subjectAltName is plain old pine.

You may have a try at imaps://imap.math.uni-bonn.de (or at https://www.math.uni-bonn.de in case you want to check HTTPS clients). The certificates are NOT self-signed, but signed with a custom CA cert (to be found at http://www.math.uni-bonn.de/people/support/MathInstUniBonn.pem in case you care).

Charles Marcus

29 Sep 29 Sep

3:53 p.m.

New subject: [Dovecot] Subject Alternativee Names

On 9/28/2009 12:41 PM, Edgar Fuß wrote:

...

...
There is a way to add 'alternate names'

...

Subject Altenative Names.

...

...
but I don't think TBird (or most other Clients) will recognize them.

...

The only client I know of NOT suporting subjectAltName is plain old pine.

Cool... thanks! I'll give it a try then soon...

Best regards,

Charles

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13 comments

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participants (8)

aja-lists
Charles Marcus
Christian Schmidt
Ed W
Edgar Fuß
Josep L. Guallar-Esteve
Patrick Nagel
Richard Hobbs