On 2021 Jul 29, 10:01, Viktor Dukhovni wrote:
>
>
> > On 29 Jul 2021, at 8:17 am, raf <post...@raf.org> wrote:
> >
> > The Rhenus email did say:
> >
> > "...must be sent with the TLS 1.2 protocol or higher.
> > Any mail received without fulfilling this condition
> > will be rejected by our server."
> >
> > That second sentence sounds to me like a definite
> > statement that an SMTP connection that doesn't initiate
> > STARTTLS will not be able to send email. At least, I
> > can't see how else to interpret those words.
>
> The simplest thing they could do is just disable TLS 1.0.
> This would also comply with some brain in neutral audit.
>
> My money is on brain in neutral, as opposed to a carefully
> considered risk assessment in which they've concluded that
> they only receive legitimate email from TLS-1.2-capable
> senders. I may be wrong in this case, but my "b[ae]tting
> average" would generally be quite high in general.
>
> So expect a poorly thought out simple TLS policy, rather
> than a carefully considered comprehensive policy.
Hello, to follow up on this issue regarding Rhenus.com and TLS 1.2,
I confirm that mail flow to them without using the STARTTLS verb in the
SMTP transaction, is working fine. So it looks like plain text SMTP is
still allowed by their publicly-referenced SMTP servers.
So at first sight it looks like Viktor's interpretation of Rhenus'
communication was right.
However, upon further inspection, it appears that the publicly-referenced
SMTP servers of Rhenus.com are still supporting TLS 1.0, which could be
read as they not following through with their original notice of only
supporting TLS 1.2 in SMTP from August 1st onwards.
If, from a TLS 1.0-only host I run this command, I get this:
$ openssl s_client -connect mx-in2.de.rhenus.com:25 -starttls smtp
(...snip...)
fnyzu7HSqPgBNKe6kmjaWNFZOdfopGvl7wEjU84NsL8y3rZ3gYm5WGtyw92ryWLj
pWIMifIkDTXFMOivRPW2p+29gkXBhl3mGlLlBGrmpKr8yjRfvDZDXi8SzHsMPECX
tTS3eAqF8viudEmzB7OqRyyICi3wlH8em7hOVwsPpxU=
-----END CERTIFICATE-----
subject=/CN=*.de.rhenus.com
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=Thawte TLS RSA CA G1
---
No client certificate CA names sent
---
SSL handshake has read 4658 bytes and written 478 bytes
---
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES128-SHA
Server public key is 2048 bit
SSL-Session:
Protocol : TLSv1
Cipher : DHE-RSA-AES128-SHA
Session-ID: B047DEA0C1366F7D150DA86F0FB28E04FA41F7E54CE70391E8EFE2F864BDB80E
Session-ID-ctx:
Master-Key:
3517C702197323871960E7819DC37A576F80A4FB11A80C6EC2F71B8D9256B4BF799C6509DA7DCD26D3EAE033FAAE2A34
Key-Arg : None
Start Time: 1628863962
Timeout : 300 (sec)
Verify return code: 19 (self signed certificate in certificate chain)
---
220 mx-in2.de.rhenus.com ESMTP
421 Exceeded allowable connection time, disconnecting.
closed
---> Which means they are still supporting TLS 1.0 in SMTP.
And if I issue that same command from a TLS 1.2-supporting host, I get:
$ openssl s_client -connect mx-in2.de.rhenus.com:25 -starttls smtp
(...snip...)
fnyzu7HSqPgBNKe6kmjaWNFZOdfopGvl7wEjU84NsL8y3rZ3gYm5WGtyw92ryWLj
pWIMifIkDTXFMOivRPW2p+29gkXBhl3mGlLlBGrmpKr8yjRfvDZDXi8SzHsMPECX
tTS3eAqF8viudEmzB7OqRyyICi3wlH8em7hOVwsPpxU=
-----END CERTIFICATE-----
subject=CN = *.de.rhenus.com
issuer=C = US, O = DigiCert Inc, OU = www.digicert.com, CN = Thawte TLS RSA CA
G1
---
No client certificate CA names sent
Peer signing digest: SHA512
Peer signature type: RSA
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 4485 bytes and written 481 bytes
Verification: OK
---
New, TLSv1.2, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES128-GCM-SHA256
Session-ID: FB20C4A6328728D31B5BEB618879C67F33C9BFA8BF51CFC686D3B5EEEBFF51A7
Session-ID-ctx:
Master-Key:
CC8AA3D2CCEB7F7873CC6C8252210216E93CD74F55F6E0AFCC5FAAB81C707AADEADC0D07AC17F94ACE546D264CD260D2
PSK identity: None
PSK identity hint: None
SRP username: None
TLS session ticket lifetime hint: 300 (seconds)
TLS session ticket:
0000 - 61 d1 9e cc d6 ab 6a 48-e9 ba f9 1c b2 1a 57 05 a.....jH......W.
0010 - ce 9f e4 f8 d7 42 48 52-2e 55 ff 1b ee d7 6b a9 .....BHR.U....k.
0020 - fa 2d 41 a6 8a f3 a5 70-5e ef 0d 1c f9 93 8a de .-A....p^.......
0030 - f7 ed 04 b4 d2 34 b3 e3-65 bd 82 c4 03 cb 69 c1 .....4..e.....i.
0040 - fc 3f 3d 33 17 6f 59 b6-82 ac 77 f3 c1 6c 9e 68 .?=3.oY...w..l.h
0050 - d6 1e 73 e9 76 24 3a 18-40 00 6d 97 0b 86 95 9b ..s.v$:.@.m.....
0060 - 20 a4 f6 d0 2a d1 ed 17-9f 78 5c 7c 2b 04 89 3b ...*....x\|+..;
0070 - dc ea 6d d5 d9 28 52 67-35 11 43 2e 51 f4 f5 0f ..m..(Rg5.C.Q...
0080 - 36 4e 89 8a 81 79 8c f1-50 c0 dd ec aa 66 26 ec 6N...y..P....f&.
0090 - fa de 54 3c 1a fe 05 68-12 2c ae 17 6a f0 20 2b ..T<...h.,..j. +
00a0 - d2 ba 0a 9a a8 c8 a6 18-65 69 19 f3 46 7e c5 9f ........ei..F~..
00b0 - 0e 07 0e 7c 39 05 15 2d-24 18 5d ce 81 63 a6 40 ...|9..-$.]..c.@
00c0 - 32 e0 1f 72 3a 9a 9d a8-44 fc 02 d8 e9 cf 67 02 2..r:...D.....g.
Start Time: 1628863075
Timeout : 7200 (sec)
Verify return code: 0 (ok)
Extended master secret: no
---
250 STARTTLS
421 Exceeded allowable connection time, disconnecting.
closed
---> Which means they also support TLS 1.2 in SMTP.
Perhaps they re-evaluated their decision and are keeping TLS 1.0 for
SMTP? Who knows!
Regards,
--
Josh Good
