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when suggesting CAA records for a domain, suggest variants that bind to the account id and with validation methods used by mox

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should prevent potential mitm attacks. especially when done close to the
machine itself (where a http/tls challenge is intercepted to get a valid
certificate), as seen on the internet last month.
This commit is contained in:
Mechiel Lukkien
2023-12-21 15:16:30 +01:00
parent ca97293cb2
commit db3fef4981
11 changed files with 123 additions and 28 deletions
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73
mox-/admin.go
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@ -458,10 +458,16 @@ func WebserverConfigSet(ctx context.Context, domainRedirects map[string]string,
// DomainRecords returns text lines describing DNS records required for configuring
// a domain.
func DomainRecords(domConf config.Domain, domain dns.Domain, hasDNSSEC bool) ([]string, error) {
//
// If certIssuerDomainName is set, CAA records to limit TLS certificate issuance to
// that caID will be suggested. If acmeAccountURI is also set, CAA records also
// restricting issuance to that account ID will be suggested.
func DomainRecords(domConf config.Domain, domain dns.Domain, hasDNSSEC bool, certIssuerDomainName, acmeAccountURI string) ([]string, error) {
d := domain.ASCII
h := Conf.Static.HostnameDomain.ASCII
// The first line with ";" is used by ../testdata/integration/moxacmepebble.sh and
// ../testdata/integration/moxmail2.sh for selecting DNS records
records := []string{
"; Time To Live of 5 minutes, may be recognized if importing as a zone file.",
"; Once your setup is working, you may want to increase the TTL.",
@ -471,15 +477,15 @@ func DomainRecords(domConf config.Domain, domain dns.Domain, hasDNSSEC bool) ([]
if public, ok := Conf.Static.Listeners["public"]; ok && public.TLS != nil && (len(public.TLS.HostPrivateRSA2048Keys) > 0 || len(public.TLS.HostPrivateECDSAP256Keys) > 0) {
records = append(records,
"; DANE: These records indicate that a remote mail server trying to deliver email",
"; with SMTP (TCP port 25) must verify the TLS certificate with DANE-EE (3), based",
"; on the certificate public key (\"SPKI\", 1) that is SHA2-256-hashed (1) to the",
"; hexadecimal hash. DANE-EE verification means only the certificate or public",
"; key is verified, not whether the certificate is signed by a (centralized)",
"; certificate authority (CA), is expired, or matches the host name.",
";",
"; NOTE: Create the records below only once: They are for the machine, and apply",
"; to all hosted domains.",
`; DANE: These records indicate that a remote mail server trying to deliver email`,
`; with SMTP (TCP port 25) must verify the TLS certificate with DANE-EE (3), based`,
`; on the certificate public key ("SPKI", 1) that is SHA2-256-hashed (1) to the`,
`; hexadecimal hash. DANE-EE verification means only the certificate or public`,
`; key is verified, not whether the certificate is signed by a (centralized)`,
`; certificate authority (CA), is expired, or matches the host name.`,
`;`,
`; NOTE: Create the records below only once: They are for the machine, and apply`,
`; to all hosted domains.`,
)
if !hasDNSSEC {
records = append(records,
@ -666,13 +672,48 @@ func DomainRecords(domConf config.Domain, domain dns.Domain, hasDNSSEC bool) ([]
fmt.Sprintf(`_submission._tcp.%s. SRV 0 1 587 .`, d),
fmt.Sprintf(`_pop3._tcp.%s. SRV 0 1 110 .`, d),
fmt.Sprintf(`_pop3s._tcp.%s. SRV 0 1 995 .`, d),
"",
"; Optional:",
"; You could mark Let's Encrypt as the only Certificate Authority allowed to",
"; sign TLS certificates for your domain.",
fmt.Sprintf("%s. CAA 0 issue \"letsencrypt.org\"", d),
)
if certIssuerDomainName != "" {
// ../rfc/8659:18 for CAA records.
records = append(records,
"",
"; Optional:",
"; You could mark Let's Encrypt as the only Certificate Authority allowed to",
"; sign TLS certificates for your domain.",
fmt.Sprintf(`%s. CAA 0 issue "%s"`, d, certIssuerDomainName),
)
if acmeAccountURI != "" {
// ../rfc/8657:99 for accounturi.
// ../rfc/8657:147 for validationmethods.
records = append(records,
";",
"; Optionally limit certificates for this domain to the account ID and methods used by mox.",
fmt.Sprintf(`;; %s. CAA 0 issue "%s; accounturi=%s; validationmethods=tls-alpn-01,http-01"`, d, certIssuerDomainName, acmeAccountURI),
";",
"; Or alternatively only limit for email-specific subdomains, so you can use",
"; other accounts/methods for other subdomains.",
fmt.Sprintf(`;; autoconfig.%s. CAA 0 issue "%s; accounturi=%s; validationmethods=tls-alpn-01,http-01"`, d, certIssuerDomainName, acmeAccountURI),
fmt.Sprintf(`;; mtasts.%s. CAA 0 issue "%s; accounturi=%s; validationmethods=tls-alpn-01,http-01"`, d, certIssuerDomainName, acmeAccountURI),
)
if strings.HasSuffix(h, "."+d) {
records = append(records,
";",
"; And the mail hostname.",
fmt.Sprintf(`;; %-*s CAA 0 issue "%s; accounturi=%s; validationmethods=tls-alpn-01,http-01"`, 20-3+len(d), h+".", certIssuerDomainName, acmeAccountURI),
)
}
} else {
// The string "will be suggested" is used by
// ../testdata/integration/moxacmepebble.sh and ../testdata/integration/moxmail2.sh
// as end of DNS records.
records = append(records,
";",
"; Note: After starting up, once an ACME account has been created, CAA records",
"; that restrict issuance to the account will be suggested.",
)
}
}
return records, nil
}