On Sun, Jan 09, 2022 at 10:22:36PM +0100, Joachim Lindenberg wrote: > I configured my Email server (actually a mailcow-dockerized which in > turn uses postfix) to enforce TLS for outbound mail. Obviously that > will fail occasionally, but I also have a daemon watching the postfix > queue and alerting me. Kind of works for me. Ok, while subscribing to > this mailing list I had to add two more exceptions, because this > mailing list uses an untrusted certificate > (https://www.checktls.com/TestReceiver?LEVEL=DETAIL > <https://www.checktls.com/TestReceiver?LEVEL=DETAIL&EMAIL=majord...@postfix.org> > &EMAIL=majord...@postfix.org). Aren´t letsencrypt certs cheap > enough in order to get rid of untrusted certificates?
The certificate is fine, the actual problem is that mail.cloud9.net does not include the intermediate issuer certificate in its certificate chain, which consists of justs the leaf certificate. The issuer cert for "Sectigo RSA Domain Validation Secure Server CA" would be needed to complete the chain to a WebPKI trust anchor (root CA). Sectigo sure go to a lot of trouble to make obtaining the intermediate certificate a laborious process, I am attaching a copy, along with a "just in case" cross-cert for its issuer. > When reading the documentation page > http://www.postfix.org/TLS_README.html#client_tls however I am > wondering what the difference between options “verify” and “secure” > is. By default, "verify" checks whether the presented certificate matches the MX hostname, which is typically obtained via unauthenticated DNS lookups, so easily subject to active (MiTM) attacks. With "secure" the presented certificate is checked agains the nexthop domain (typically the domain part of the recipient address). This is not subject to attacks via forged DNS replies. However, typically the MX host certificate will not have the recipient domain as one of its SANs unless the domain is self-hosted. For example, "postfix.org" does not appear in the certificate of "mail.cloud9.net". So "secure" is often not an option, unless you specify explicit non-default matching criteria, at which point the difference between "secure" and "verify" vanishes, they only differ in the default name matching patterns. > I read it several times and got the message, I should not use > either, but what exactly is the difference remained unclear to me. Is > “DNS forgery resistant server certificate verification“ defined in > some RFC or other document I am not aware of? It is defined (explained) in TLS_README. Sorry it was not as clear as you would like. -- Viktor.
subject=C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited, CN = Sectigo RSA Domain Validation Secure Server CA issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority -----BEGIN CERTIFICATE----- MIIGEzCCA/ugAwIBAgIQfVtRJrR2uhHbdBYLvFMNpzANBgkqhkiG9w0BAQwFADCB iDELMAkGA1UEBhMCVVMxEzARBgNVBAgTCk5ldyBKZXJzZXkxFDASBgNVBAcTC0pl cnNleSBDaXR5MR4wHAYDVQQKExVUaGUgVVNFUlRSVVNUIE5ldHdvcmsxLjAsBgNV BAMTJVVTRVJUcnVzdCBSU0EgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkwHhcNMTgx MTAyMDAwMDAwWhcNMzAxMjMxMjM1OTU5WjCBjzELMAkGA1UEBhMCR0IxGzAZBgNV BAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEYMBYGA1UE ChMPU2VjdGlnbyBMaW1pdGVkMTcwNQYDVQQDEy5TZWN0aWdvIFJTQSBEb21haW4g VmFsaWRhdGlvbiBTZWN1cmUgU2VydmVyIENBMIIBIjANBgkqhkiG9w0BAQEFAAOC AQ8AMIIBCgKCAQEA1nMz1tc8INAA0hdFuNY+B6I/x0HuMjDJsGz99J/LEpgPLT+N TQEMgg8Xf2Iu6bhIefsWg06t1zIlk7cHv7lQP6lMw0Aq6Tn/2YHKHxYyQdqAJrkj eocgHuP/IJo8lURvh3UGkEC0MpMWCRAIIz7S3YcPb11RFGoKacVPAXJpz9OTTG0E oKMbgn6xmrntxZ7FN3ifmgg0+1YuWMQJDgZkW7w33PGfKGioVrCSo1yfu4iYCBsk Haswha6vsC6eep3BwEIc4gLw6uBK0u+QDrTBQBbwb4VCSmT3pDCg/r8uoydajotY uK3DGReEY+1vVv2Dy2A0xHS+5p3b4eTlygxfFQIDAQABo4IBbjCCAWowHwYDVR0j BBgwFoAUU3m/WqorSs9UgOHYm8Cd8rIDZsswHQYDVR0OBBYEFI2MXsRUrYrhd+mb +ZsF4bgBjWHhMA4GA1UdDwEB/wQEAwIBhjASBgNVHRMBAf8ECDAGAQH/AgEAMB0G A1UdJQQWMBQGCCsGAQUFBwMBBggrBgEFBQcDAjAbBgNVHSAEFDASMAYGBFUdIAAw CAYGZ4EMAQIBMFAGA1UdHwRJMEcwRaBDoEGGP2h0dHA6Ly9jcmwudXNlcnRydXN0 LmNvbS9VU0VSVHJ1c3RSU0FDZXJ0aWZpY2F0aW9uQXV0aG9yaXR5LmNybDB2Bggr BgEFBQcBAQRqMGgwPwYIKwYBBQUHMAKGM2h0dHA6Ly9jcnQudXNlcnRydXN0LmNv bS9VU0VSVHJ1c3RSU0FBZGRUcnVzdENBLmNydDAlBggrBgEFBQcwAYYZaHR0cDov L29jc3AudXNlcnRydXN0LmNvbTANBgkqhkiG9w0BAQwFAAOCAgEAMr9hvQ5Iw0/H ukdN+Jx4GQHcEx2Ab/zDcLRSmjEzmldS+zGea6TvVKqJjUAXaPgREHzSyrHxVYbH 7rM2kYb2OVG/Rr8PoLq0935JxCo2F57kaDl6r5ROVm+yezu/Coa9zcV3HAO4OLGi H19+24rcRki2aArPsrW04jTkZ6k4Zgle0rj8nSg6F0AnwnJOKf0hPHzPE/uWLMUx RP0T7dWbqWlod3zu4f+k+TY4CFM5ooQ0nBnzvg6s1SQ36yOoeNDT5++SR2RiOSLv xvcRviKFxmZEJCaOEDKNyJOuB56DPi/Z+fVGjmO+wea03KbNIaiGCpXZLoUmGv38 sbZXQm2V0TP2ORQGgkE49Y9Y3IBbpNV9lXj9p5v//cWoaasm56ekBYdbqbe4oyAL l6lFhd2zi+WJN44pDfwGF/Y4QA5C5BIG+3vzxhFoYt/jmPQT2BVPi7Fp2RBgvGQq 6jG35LWjOhSbJuMLe/0CjraZwTiXWTb2qHSihrZe68Zk6s+go/lunrotEbaGmAhY LcmsJWTyXnW0OMGuf1pGg+pRyrbxmRE1a6Vqe8YAsOf4vmSyrcjC8azjUeqkk+B5 yOGBQMkKW+ESPMFgKuOXwIlCypTPRpgSabuY0MLTDXJLR27lk8QyKGOHQ+SwMj4K 00u/I5sUKUErmgQfky3xxzlIPK1aEn8= -----END CERTIFICATE----- subject=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority issuer=C = GB, ST = Greater Manchester, L = Salford, O = Comodo CA Limited, CN = AAA Certificate Services -----BEGIN CERTIFICATE----- MIIFgTCCBGmgAwIBAgIQOXJEOvkit1HX02wQ3TE1lTANBgkqhkiG9w0BAQwFADB7 MQswCQYDVQQGEwJHQjEbMBkGA1UECAwSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYD VQQHDAdTYWxmb3JkMRowGAYDVQQKDBFDb21vZG8gQ0EgTGltaXRlZDEhMB8GA1UE AwwYQUFBIENlcnRpZmljYXRlIFNlcnZpY2VzMB4XDTE5MDMxMjAwMDAwMFoXDTI4 MTIzMTIzNTk1OVowgYgxCzAJBgNVBAYTAlVTMRMwEQYDVQQIEwpOZXcgSmVyc2V5 MRQwEgYDVQQHEwtKZXJzZXkgQ2l0eTEeMBwGA1UEChMVVGhlIFVTRVJUUlVTVCBO ZXR3b3JrMS4wLAYDVQQDEyVVU0VSVHJ1c3QgUlNBIENlcnRpZmljYXRpb24gQXV0 aG9yaXR5MIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEAgBJlFzYOw9sI s9CsVw127c0n00ytUINh4qogTQktZAnczomfzD2p7PbPwdzx07HWezcoEStH2jnG vDoZtF+mvX2do2NCtnbyqTsrkfjib9DsFiCQCT7i6HTJGLSR1GJk23+jBvGIGGqQ Ijy8/hPwhxR79uQfjtTkUcYRZ0YIUcuGFFQ/vDP+fmyc/xadGL1RjjWmp2bIcmfb IWax1Jt4A8BQOujM8Ny8nkz+rwWWNR9XWrf/zvk9tyy29lTdyOcSOk2uTIq3XJq0 tyA9yn8iNK5+O2hmAUTnAU5GU5szYPeUvlM3kHND8zLDU+/bqv50TmnHa4xgk97E xwzf4TKuzJM7UXiVZ4vuPVb+DNBpDxsP8yUmazNt925H+nND5X4OpWaxKXwyhGNV icQNwZNUMBkTrNN9N6frXTpsNVzbQdcS2qlJC9/YgIoJk2KOtWbPJYjNhLixP6Q5 D9kCnusSTJV882sFqV4Wg8y4Z+LoE53MW4LTTLPtW//e5XOsIzstAL81VXQJSdhJ WBp/kjbmUZIO8yZ9HE0XvMnsQybQv0FfQKlERPSZ51eHnlAfV1SoPv10Yy+xUGUJ 5lhCLkMaTLTwJUdZ+gQek9QmRkpQgbLevni3/GcV4clXhB4PY9bpYrrWX1Uu6lzG KAgEJTm4Diup8kyXHAc/DVL17e8vgg8CAwEAAaOB8jCB7zAfBgNVHSMEGDAWgBSg EQojPpbxB+zirynvgqV/0DCktDAdBgNVHQ4EFgQUU3m/WqorSs9UgOHYm8Cd8rID ZsswDgYDVR0PAQH/BAQDAgGGMA8GA1UdEwEB/wQFMAMBAf8wEQYDVR0gBAowCDAG BgRVHSAAMEMGA1UdHwQ8MDowOKA2oDSGMmh0dHA6Ly9jcmwuY29tb2RvY2EuY29t L0FBQUNlcnRpZmljYXRlU2VydmljZXMuY3JsMDQGCCsGAQUFBwEBBCgwJjAkBggr BgEFBQcwAYYYaHR0cDovL29jc3AuY29tb2RvY2EuY29tMA0GCSqGSIb3DQEBDAUA A4IBAQAYh1HcdCE9nIrgJ7cz0C7M7PDmy14R3iJvm3WOnnL+5Nb+qh+cli3vA0p+ rvSNb3I8QzvAP+u431yqqcau8vzY7qN7Q/aGNnwU4M309z/+3ri0ivCRlv79Q2R+ /czSAaF9ffgZGclCKxO/WIu6pKJmBHaIkU4MiRTOok3JMrO66BQavHHxW/BBC5gA CiIDEOUMsfnNkjcZ7Tvx5Dq2+UUTJnWvu6rvP3t3O9LEApE9GQDTF1w52z97GA1F zZOFli9d31kWTz9RvdVFGD/tSo7oBmF0Ixa1DVBzJ0RHfxBdiSprhTEUxOipakyA vGp4z7h/jnZymQyd/teRCBaho1+V -----END CERTIFICATE-----
