Strategies for protecting IMAP (e.g. MFA)
André Rodier
andre at rodier.me
Mon Nov 15 12:40:16 UTC 2021
On 15/11/2021 11:52, Arjen de Korte wrote:
> Citeren Benny Pedersen <me at junc.eu>:
>
>> On 2021-11-14 20:26, Matthew Richardson wrote:
>>> On Sun, 14 Nov 2021 08:12:53 -0800, Michael Peddemors wrote:-
>>>
>>>> And there are RBL's now for know IP(s) used by IMAP hackers, including
>>>> SpamRats RATS-AUTH that can assist in reducing those attacks.
>>>
>>> Looking at https://www.spamrats.com/rats-auth.php the "Example Usage in
>>> Dovecot" says "PLEASE UPDATE".
>>>
>>> How would one use a DNSBL like this in Dovecot to reject IMAP
>>> connections
>>> from listed IPs?
>>
>> submission inet n - y - - smtpd
>> -o smtpd_tls_security_level=encrypt
>> -o smtpd_sasl_auth_enable=yes
>> -o smtpd_delay_reject=no
>> -o { smtpd_client_restrictions = reject_rbl_client
>> auth.spamrats.com=127.0.0.39, permit }
>> -o { smtpd_relay_restrictions = permit_mynetworks,
>> permit_sasl_authenticated, reject }
>
> This is not an answer to the question, this is Postfix syntax.
>
>> openRelay, dont do it
>
> In what way would this create an open relay exactly? The 'permit' at the
> end of the 'smtpd_client_restrictions' only means that the client is
> accepted, not that other smtpd restrictions are lifted.
>
>> resolved version
>>
>> submission inet n - y - - smtpd
>> -o smtpd_tls_security_level=encrypt
>> -o smtpd_sasl_auth_enable=yes
>> -o smtpd_delay_reject=no
>> -o { smtpd_relay_restrictions = reject_rbl_client
>> auth.spamrats.com=127.0.0.39, permit_mynetworks,
>> permit_sasl_authenticated, reject }
>
> Although syntactically correct, it is confusing at best to put client
> restrictions in another place than smtpd_client_restrictions. Especially
> with 'smtpd_delay_reject=no' in effect you'd only reject after receiving
> 'RCPT TO', which is evaluated after 'smtpd_client_restrictions' and
> 'smtpd_helo_restrictions' during the SMTP transfer.
>
>> order do matter
>
> Indeed.
>
>
>
Perhaps I was not clear in my last message. Have a look to this
documentation:
https://homebox.readthedocs.io/en/latest/email-access-monitoring/
I am available if you have any question to implement something similar
yourself. Extending the system to add a second factor authentication is
probably easy enough.
Kind regards,
André
--
𝓐𝓡 - André Rodier
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