On 22.08.2017 03:56, Peter wrote:>>> Lest anyone think STARTTLS MITM doesn't happen, >>> >>> https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ > Right, the attack does happen, but it can be prevented by properly > configuring the server and client.Dovecot, by default, requires STARTTLS before accepting plaintext authentication when SSL is configured and you are not connecting from localhost. You can verify this by telnetting to port 143 from somewhere else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you have enabled something like cram-md5. I think postfix, by default, will also prevent authentication without transport security. Also, you should probably using 587/tcp (submission) for sending mail, instead of 25. Some reputable ISPs prevent connecting to random MX servers to port 25 to make life harder for spambots. Aki
On Tue, 22 Aug 2017, Aki Tuomi wrote:> else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you > have enabled something like cram-md5.Hi, exactly, this is the reason, why plain-text is still needed. You don't need encryption for authentication, if you have secure authentication. Without knowing original password, the MITM cannot generate correct hash for login, so the connection can be plain-text. Of cource, if you then download your emails, the MITM can still read these emails too, if these emails are plain-text (not encrypted using e.g. SMIME or GPG). But he cannot misuse your login. Regards, Robert Wolf.
On 22/08/17 18:24, Aki Tuomi wrote:> Dovecot, by default, requires STARTTLS before accepting plaintext > authentication when SSL is configured and you are not connecting from > localhost. You can verify this by telnetting to port 143 from somewhere > else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you > have enabled something like cram-md5. > > I think postfix, by default, will also prevent authentication without > transport security.No: $ postconf -d smtpd_tls_auth_only smtpd_tls_auth_only = no The commented submission service in master.cf contains it, though, so if you uncomment the service as a whole it will be set: # -o smtpd_tls_auth_only=yes> Also, you should probably using 587/tcp (submission) for sending mail, > instead of 25. Some reputable ISPs prevent connecting to random MX > servers to port 25 to make life harder for spambots.Right, you should never use port 25 for submission, for several reasons. Peter
On 22/08/17 20:07, Robert Wolf wrote:> On Tue, 22 Aug 2017, Aki Tuomi wrote: > >> else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you >> have enabled something like cram-md5. > > exactly, this is the reason, why plain-text is still needed. You don't need > encryption for authentication, if you have secure authentication. Without > knowing original password, the MITM cannot generate correct hash for login, so > the connection can be plain-text.In order to support non plain-text login types the passwords themselves have to be stored in plain-text. If you use PLAIN but only allow authentication over a secure channel then you get the best of both worlds, you can store your passwords as a hash and they are not transmitted as plain text over the internet. Peter