Stopping login via "nologin" parameter

[J Doe]

> On Jul 19, 2018, at 6:49 PM, J Doe <general at nativemethods.com <mailto:general at nativemethods.com>> wrote:
> 
> Hello,
> 
> I have a basic e-mail server with Postfix 3.1 and Dovecot 2.2.22.
> 
> I am using a passwd-file for both userdb and passdb:
> 
>    /etc/dovecot/dovecot.conf
>        userdb {
>            driver = passwd-file
>            args = /etc/dovecot/passwd
>        }
> 
>        passdb {
>            driver = passwd-file
>            args = /etc/dovecot/passwd
>        }
>    }
> 
> In the passwd file, I want to have user account names for SMTP SASL AUTH and IMAP that are NOT e-mail addresses.
> 
> For example, employee one of ABC corp would have a SMTP SASL AUTH/IMAP account name in the form: abc_company_employeeid (for example: abc_company_03284).  The idea behind that is that I do not want someone outside of the company to be able to know the first half of the username and password pair just because they have an employee's e-mail address.
> 
> For the e-mail address I specify something like: bob at abc.com <mailto:bob at abc.com> however I never want someone to be able to login via their e-mail address.  Originally, I specified the password field as empty, with the understanding being that the default encryption of a password is {CRYPT}.  Since crypt() cannot output a null string, this meant that there was never a valid password.
> 
> So passwd looked like this:
> 
>    /etc/dovecot/passwd
>        # SMTP SASL AUTH and IMAP accounts
>        abc_company_03284:::::::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>
> 
>        # IMAP
>        bob at abc.com <mailto:bob at abc.com>:vmail:vmail::/home/vmail/bob::userdb_maill=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>
> 
> I tested SMTP SASL AUTH and IMAP via the openssl s_client and can confirm that I can login and send e-mail as well as retrieve mail only via the: abc_company_03284 account, but because an empty password field isn’t mentioned on the Dovecot wiki, I was wondering if I should add “nologin” to explicitly make it impossible for: bob at abc.com <mailto:bob at abc.com>.  “nologin” was mentioned to me in a previous e-mail to this list.
> 
> So passwd would now look like this:
> 
>    /etc/dovecot/passwd
>        # SMTP SASL AUTH and IMAP accounts
>        abc_company_03284:::::::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>
> 
>        # IMAP
>        bob at abc.com <mailto:bob at abc.com>:vmail:vmail::/home/vmail/bob::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284> nologin
> 
> I restarted Dovecot and tested this with openssl s_client for SMTP SASL AUTH and IMAP, but just wanted to make sure that this STOPS ANY LOGINS via the e-mail address: bob at abc.com <mailto:bob at abc.com> ?
> 
> Thanks,
> 
> - J

Hi list,

I believe I’ve found the solution I’m looking for.

I use one passwd-file for SMTP SASL AUTH, IMAP and LMTP from a Postfix 3.1 server to a Dovecot 2.2.22 server.

    /etc/dovecot/dovecot.conf
        userdb {
           driver = passwd-file
           args = /etc/dovecot/passwd
       }

       passdb {
           driver = passwd-file
           args = /etc/dovecot/passwd
       }
   }

The passwd file contains one test user.  The test user’s SMTP SASL AUTH and IMAP account name is: “abc_company_03284" and has a password of “password”.
The e-mail address of that user is "bob at abc.com <mailto:bob at abc.com>".  I don’t have the SMTP SASL AUTH and IMAP account name set to “bob at abc.com <mailto:bob at abc.com>" because I don’t want someone to try to login by assuming the SMTP SASL AUTH/IMAP account name is the user’s e-mail address.

    /etc/dovecot/passwd
        # SMTP SASL AUTH and IMAP information
        abc_company_03284:{PLAIN}password::::::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>

        # LMTP
        bob at abc.com <mailto:bob at abc.com>:{PLAIN}password:vmail:vmail:/home/vmail/bob::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>

If I test logging on via SMTP SASL AUTH and IMAP via the openssl s_client, I can log on using an account name of “bob at abc.com" and a password of “password”, as expected.

To stop someone from logging on via their e-mail address, I place “fail” [1] at the end INSTEAD OF “nologin”:

    /etc/dovecot/passwd
        # SMTP SASL AUTH and IMAP information
        abc_company_03284:{PLAIN}password::::::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>

        # LMTP
        bob at abc.com <mailto:bob at abc.com>:{PLAIN}password:vmail:vmail:/home/vmail/bob::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284> fail 

If I then restart Postfix and Dovecot and attempt to login via SMTP SASL AUTH and IMAP via the openssl s_client with an account name of “bob at abc.com <mailto:bob at abc.com>” and use a password of “password”, it now fails password lookup in both instances.  Because of the “fail” command, the password field I used for testing with the “bob at abc.com <mailto:bob at abc.com>" account is irrelevant and I can remove it.  Therefore my final passwd file is:

    /etc/dovecot/passwd
        # SMTP SASL AUTH and IMAP information
        abc_company_03284:{PLAIN}password::::::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>

        # LMTP
        bob at abc.com <mailto:bob at abc.com>::vmail:vmail:/home/vmail/bob::userdb_mail=maildir:/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284> fail 

Sending a test e-mail to “bob at abc.com <mailto:bob at abc.com>” confirms that the user’s e-mail is received and stored in: "/var/mail/vhosts/abc.com/abc_company_03284 <http://abc.com/abc_company_03284>”, which means LMTP is working.

Can anyone confirm that I am correct about this ?  I want to be sure that is now:

    1) Impossible to login via SMTP SASL AUTH and IMAP using the e-mail address “bob at abc.com <mailto:bob at abc.com>”.
    2) Only possible to login via SMTP SASL AUTH and IMAP using the account name “abc_company_03284” and a password of “password"

Thanks,

- J

Sources:

[1] https://wiki2.dovecot.org/PasswordDatabase/ExtraFields <https://wiki2.dovecot.org/PasswordDatabase/ExtraFields> and see “fail"
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