Folks, mail-providers especially, a heads-up: I've committed a change for the next release of Exim (not imminent) which is a "default configuration file" change to the suggested configuration for talking to mail smarthosts.
The changes are all around TLS. The new Exim suggested smarthost configuration: 1. Requires TLS, always, if the Exim binary was built with TLS support. 2. Sends TLS SNI matching the configured smarthost name, which should be whatever folks have told their customers to use; there are no DANE/security issues here, this should be a static name, from a trustworthy path, so what the ISP/mail-provider tells people to use damned well should be verifiable. 3. Will actually verify the certificate chain and hostname. With a fallback so that if people have to comment that out, then they'll at least be logging verification status. 4. Stronger TLS ciphers specified (see below). My text to exim-users just now includes: } Because many mail-clients are configured to talk directly to ISP } smarthosts and mail-clients usually enable TLS with decent verification } (or at least, the ones I use do), there _shouldn't_ be any issues. } But if there are, then they're likely to be: } } 1. Mail-provider does not provide STARTTLS on their smarthost. In 2018. } Seriously? Find a new mail-provider. } } 2. Certificate does not verify. File a Support request with the } mail-provider to get it fixed. } In 2018? Seriously consider a new mail-provider. } } 3. You have to comment out the tls_require_ciphers because the } mail-provider is running with really poor TLS support. } File a Support request. If they don't fix this quickly, then } consider a new mail-provider. The new smarthost TLS cipher configuration is currently: * for OpenSSL: HIGH:@STRENGTH * for GnuTLS: NONE:+VERS-TLS1.2:SECURE192 At this point, I can't commit to getting an OpenSSL revamp in, to let people specify TLS minimum versions etc, so the above is simply "what things are supported now". Everything in the new default configuration should work with existing versions of Exim. If I get the OpenSSL revamp in, then the OpenSSL suggested configuration will also specify TLS1.2 as the minimum. I seriously considered mandating a PFS suite in the new default, but haven't yet done so. That might change before the release. None of the demands here are particularly strong, by the standards of web security. There's no reason for email to a known specified hostname to have to be any weaker. The rest of this mail is simply lists of TLS cipher suites which correspond to the above. If your customer-facing smarthost can't negotiate at least one of these ciphers, then please consider remedying that. -Phil --------------------------8< GnuTLS 3.5.18 >8--------------------------- # using sample code from GnuTLS Manual, 7.4.3 $ ./gnutls-list-priostring-ciphers 'NONE:+VERS-TLS1.2:SECURE192' Cipher suites for NONE:+VERS-TLS1.2:SECURE192 TLS_ECDHE_ECDSA_AES_256_GCM_SHA384 0xc0, 0x2c TLS1.2 TLS_ECDHE_ECDSA_CAMELLIA_256_GCM_SHA384 0xc0, 0x87 TLS1.2 TLS_ECDHE_ECDSA_CHACHA20_POLY1305 0xcc, 0xa9 TLS1.2 TLS_ECDHE_ECDSA_AES_256_CBC_SHA384 0xc0, 0x24 TLS1.2 TLS_ECDHE_ECDSA_CAMELLIA_256_CBC_SHA384 0xc0, 0x73 TLS1.2 TLS_ECDHE_ECDSA_AES_256_CCM 0xc0, 0xad TLS1.2 TLS_ECDHE_RSA_AES_256_GCM_SHA384 0xc0, 0x30 TLS1.2 TLS_ECDHE_RSA_CAMELLIA_256_GCM_SHA384 0xc0, 0x8b TLS1.2 TLS_ECDHE_RSA_CHACHA20_POLY1305 0xcc, 0xa8 TLS1.2 TLS_ECDHE_RSA_AES_256_CBC_SHA384 0xc0, 0x28 TLS1.2 TLS_ECDHE_RSA_CAMELLIA_256_CBC_SHA384 0xc0, 0x77 TLS1.2 TLS_RSA_AES_256_GCM_SHA384 0x00, 0x9d TLS1.2 TLS_RSA_CAMELLIA_256_GCM_SHA384 0xc0, 0x7b TLS1.2 TLS_RSA_AES_256_CBC_SHA256 0x00, 0x3d TLS1.2 TLS_RSA_CAMELLIA_256_CBC_SHA256 0x00, 0xc0 TLS1.2 TLS_RSA_AES_256_CCM 0xc0, 0x9d TLS1.2 TLS_DHE_RSA_AES_256_GCM_SHA384 0x00, 0x9f TLS1.2 TLS_DHE_RSA_CAMELLIA_256_GCM_SHA384 0xc0, 0x7d TLS1.2 TLS_DHE_RSA_CHACHA20_POLY1305 0xcc, 0xaa TLS1.2 TLS_DHE_RSA_AES_256_CBC_SHA256 0x00, 0x6b TLS1.2 TLS_DHE_RSA_CAMELLIA_256_CBC_SHA256 0x00, 0xc4 TLS1.2 TLS_DHE_RSA_AES_256_CCM 0xc0, 0x9f TLS1.2 --------------------------8< GnuTLS 3.5.18 >8--------------------------- --------------------------8< OpenSSL 1.0.2o >8-------------------------- ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA Enc=AESGCM(256) Mac=AEAD ECDHE-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AESGCM(256) Mac=AEAD ECDHE-RSA-AES256-SHA384 TLSv1.2 Kx=ECDH Au=RSA Enc=AES(256) Mac=SHA384 ECDHE-ECDSA-AES256-SHA384 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AES(256) Mac=SHA384 ECDHE-RSA-AES256-SHA SSLv3 Kx=ECDH Au=RSA Enc=AES(256) Mac=SHA1 ECDHE-ECDSA-AES256-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=AES(256) Mac=SHA1 SRP-DSS-AES-256-CBC-SHA SSLv3 Kx=SRP Au=DSS Enc=AES(256) Mac=SHA1 SRP-RSA-AES-256-CBC-SHA SSLv3 Kx=SRP Au=RSA Enc=AES(256) Mac=SHA1 SRP-AES-256-CBC-SHA SSLv3 Kx=SRP Au=SRP Enc=AES(256) Mac=SHA1 DH-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH/DSS Au=DH Enc=AESGCM(256) Mac=AEAD DHE-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=DSS Enc=AESGCM(256) Mac=AEAD DH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH/RSA Au=DH Enc=AESGCM(256) Mac=AEAD DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=RSA Enc=AESGCM(256) Mac=AEAD DHE-RSA-AES256-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AES(256) Mac=SHA256 DHE-DSS-AES256-SHA256 TLSv1.2 Kx=DH Au=DSS Enc=AES(256) Mac=SHA256 DH-RSA-AES256-SHA256 TLSv1.2 Kx=DH/RSA Au=DH Enc=AES(256) Mac=SHA256 DH-DSS-AES256-SHA256 TLSv1.2 Kx=DH/DSS Au=DH Enc=AES(256) Mac=SHA256 DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1 DHE-DSS-AES256-SHA SSLv3 Kx=DH Au=DSS Enc=AES(256) Mac=SHA1 DH-RSA-AES256-SHA SSLv3 Kx=DH/RSA Au=DH Enc=AES(256) Mac=SHA1 DH-DSS-AES256-SHA SSLv3 Kx=DH/DSS Au=DH Enc=AES(256) Mac=SHA1 DHE-RSA-CAMELLIA256-SHA SSLv3 Kx=DH Au=RSA Enc=Camellia(256) Mac=SHA1 DHE-DSS-CAMELLIA256-SHA SSLv3 Kx=DH Au=DSS Enc=Camellia(256) Mac=SHA1 DH-RSA-CAMELLIA256-SHA SSLv3 Kx=DH/RSA Au=DH Enc=Camellia(256) Mac=SHA1 DH-DSS-CAMELLIA256-SHA SSLv3 Kx=DH/DSS Au=DH Enc=Camellia(256) Mac=SHA1 AECDH-AES256-SHA SSLv3 Kx=ECDH Au=None Enc=AES(256) Mac=SHA1 ADH-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=None Enc=AESGCM(256) Mac=AEAD ADH-AES256-SHA256 TLSv1.2 Kx=DH Au=None Enc=AES(256) Mac=SHA256 ADH-AES256-SHA SSLv3 Kx=DH Au=None Enc=AES(256) Mac=SHA1 ADH-CAMELLIA256-SHA SSLv3 Kx=DH Au=None Enc=Camellia(256) Mac=SHA1 ECDH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AESGCM(256) Mac=AEAD ECDH-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(256) Mac=AEAD ECDH-RSA-AES256-SHA384 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AES(256) Mac=SHA384 ECDH-ECDSA-AES256-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256) Mac=SHA384 ECDH-RSA-AES256-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=AES(256) Mac=SHA1 ECDH-ECDSA-AES256-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256) Mac=SHA1 AES256-GCM-SHA384 TLSv1.2 Kx=RSA Au=RSA Enc=AESGCM(256) Mac=AEAD AES256-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA256 AES256-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA1 CAMELLIA256-SHA SSLv3 Kx=RSA Au=RSA Enc=Camellia(256) Mac=SHA1 PSK-AES256-CBC-SHA SSLv3 Kx=PSK Au=PSK Enc=AES(256) Mac=SHA1 ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AESGCM(128) Mac=AEAD ECDHE-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AESGCM(128) Mac=AEAD ECDHE-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AES(128) Mac=SHA256 ECDHE-ECDSA-AES128-SHA256 TLSv1.2 Kx=ECDH Au=ECDSA Enc=AES(128) Mac=SHA256 ECDHE-RSA-AES128-SHA SSLv3 Kx=ECDH Au=RSA Enc=AES(128) Mac=SHA1 ECDHE-ECDSA-AES128-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=AES(128) Mac=SHA1 SRP-DSS-AES-128-CBC-SHA SSLv3 Kx=SRP Au=DSS Enc=AES(128) Mac=SHA1 SRP-RSA-AES-128-CBC-SHA SSLv3 Kx=SRP Au=RSA Enc=AES(128) Mac=SHA1 SRP-AES-128-CBC-SHA SSLv3 Kx=SRP Au=SRP Enc=AES(128) Mac=SHA1 DH-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH/DSS Au=DH Enc=AESGCM(128) Mac=AEAD DHE-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=DSS Enc=AESGCM(128) Mac=AEAD DH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH/RSA Au=DH Enc=AESGCM(128) Mac=AEAD DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AESGCM(128) Mac=AEAD DHE-RSA-AES128-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AES(128) Mac=SHA256 DHE-DSS-AES128-SHA256 TLSv1.2 Kx=DH Au=DSS Enc=AES(128) Mac=SHA256 DH-RSA-AES128-SHA256 TLSv1.2 Kx=DH/RSA Au=DH Enc=AES(128) Mac=SHA256 DH-DSS-AES128-SHA256 TLSv1.2 Kx=DH/DSS Au=DH Enc=AES(128) Mac=SHA256 DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1 DHE-DSS-AES128-SHA SSLv3 Kx=DH Au=DSS Enc=AES(128) Mac=SHA1 DH-RSA-AES128-SHA SSLv3 Kx=DH/RSA Au=DH Enc=AES(128) Mac=SHA1 DH-DSS-AES128-SHA SSLv3 Kx=DH/DSS Au=DH Enc=AES(128) Mac=SHA1 DHE-RSA-CAMELLIA128-SHA SSLv3 Kx=DH Au=RSA Enc=Camellia(128) Mac=SHA1 DHE-DSS-CAMELLIA128-SHA SSLv3 Kx=DH Au=DSS Enc=Camellia(128) Mac=SHA1 DH-RSA-CAMELLIA128-SHA SSLv3 Kx=DH/RSA Au=DH Enc=Camellia(128) Mac=SHA1 DH-DSS-CAMELLIA128-SHA SSLv3 Kx=DH/DSS Au=DH Enc=Camellia(128) Mac=SHA1 AECDH-AES128-SHA SSLv3 Kx=ECDH Au=None Enc=AES(128) Mac=SHA1 ADH-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=None Enc=AESGCM(128) Mac=AEAD ADH-AES128-SHA256 TLSv1.2 Kx=DH Au=None Enc=AES(128) Mac=SHA256 ADH-AES128-SHA SSLv3 Kx=DH Au=None Enc=AES(128) Mac=SHA1 ADH-CAMELLIA128-SHA SSLv3 Kx=DH Au=None Enc=Camellia(128) Mac=SHA1 ECDH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AESGCM(128) Mac=AEAD ECDH-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(128) Mac=AEAD ECDH-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AES(128) Mac=SHA256 ECDH-ECDSA-AES128-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128) Mac=SHA256 ECDH-RSA-AES128-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=AES(128) Mac=SHA1 ECDH-ECDSA-AES128-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128) Mac=SHA1 AES128-GCM-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AESGCM(128) Mac=AEAD AES128-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA256 AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1 CAMELLIA128-SHA SSLv3 Kx=RSA Au=RSA Enc=Camellia(128) Mac=SHA1 PSK-AES128-CBC-SHA SSLv3 Kx=PSK Au=PSK Enc=AES(128) Mac=SHA1 --------------------------8< OpenSSL 1.0.2o >8--------------------------
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