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implement the plus variants of scram, to bind the authentication exchange to the tls connection

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to get the security benefits (detecting mitm attempts), explicitly configure
clients to use a scram plus variant, e.g. scram-sha-256-plus. unfortunately,
not many clients support it yet.

imapserver scram plus support seems to work with the latest imtest (imap test
client) from cyrus-sasl. no success yet with mutt (with gsasl) though.
This commit is contained in:
Mechiel Lukkien
2023-12-23 23:07:21 +01:00
parent 4701857d7f
commit e7478ed6ac
23 changed files with 690 additions and 189 deletions
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51
queue/submit.go
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@ -3,6 +3,7 @@ package queue
import (
"bytes"
"context"
"crypto/tls"
"errors"
"fmt"
"io"
@ -10,6 +11,7 @@ import (
"os"
"time"
"golang.org/x/exp/slices"
"golang.org/x/exp/slog"
"github.com/mjl-/mox/config"
@ -40,7 +42,7 @@ func deliverSubmit(qlog mlog.Log, resolver dns.Resolver, dialer smtpclient.Diale
if dialTLS {
tlsMode = smtpclient.TLSImmediate
} else if transport.STARTTLSInsecureSkipVerify {
tlsMode = smtpclient.TLSOpportunistic
tlsMode = smtpclient.TLSRequiredStartTLS
tlsPKIX = false
} else if transport.NoSTARTTLS {
tlsMode = smtpclient.TLSSkip
@ -119,26 +121,39 @@ func deliverSubmit(qlog mlog.Log, resolver dns.Resolver, dialer smtpclient.Diale
}
dialcancel()
var auth []sasl.Client
var auth func(mechanisms []string, cs *tls.ConnectionState) (sasl.Client, error)
if transport.Auth != nil {
a := transport.Auth
for _, mech := range a.EffectiveMechanisms {
switch mech {
case "PLAIN":
auth = append(auth, sasl.NewClientPlain(a.Username, a.Password))
case "CRAM-MD5":
auth = append(auth, sasl.NewClientCRAMMD5(a.Username, a.Password))
case "SCRAM-SHA-1":
auth = append(auth, sasl.NewClientSCRAMSHA1(a.Username, a.Password))
case "SCRAM-SHA-256":
auth = append(auth, sasl.NewClientSCRAMSHA256(a.Username, a.Password))
default:
// Should not happen.
qlog.Error("missing smtp authentication mechanisms implementation", slog.String("mechanism", mech))
errmsg = fmt.Sprintf("transport %s: authentication mechanisms %q not implemented", transportName, mech)
fail(ctx, qlog, m, backoff, false, dsn.NameIP{}, "", errmsg)
return
auth = func(mechanisms []string, cs *tls.ConnectionState) (sasl.Client, error) {
var supportsscramsha1plus, supportsscramsha256plus bool
for _, mech := range a.EffectiveMechanisms {
if !slices.Contains(mechanisms, mech) {
switch mech {
case "SCRAM-SHA-1-PLUS":
supportsscramsha1plus = cs != nil
case "SCRAM-SHA-256-PLUS":
supportsscramsha256plus = cs != nil
}
continue
}
if mech == "SCRAM-SHA-256-PLUS" && cs != nil {
return sasl.NewClientSCRAMSHA256PLUS(a.Username, a.Password, *cs), nil
} else if mech == "SCRAM-SHA-256" {
return sasl.NewClientSCRAMSHA256(a.Username, a.Password, supportsscramsha256plus), nil
} else if mech == "SCRAM-SHA-1-PLUS" && cs != nil {
return sasl.NewClientSCRAMSHA1PLUS(a.Username, a.Password, *cs), nil
} else if mech == "SCRAM-SHA-1" {
return sasl.NewClientSCRAMSHA1(a.Username, a.Password, supportsscramsha1plus), nil
} else if mech == "CRAM-MD5" {
return sasl.NewClientCRAMMD5(a.Username, a.Password), nil
} else if mech == "PLAIN" {
return sasl.NewClientPlain(a.Username, a.Password), nil
}
return nil, fmt.Errorf("internal error: unrecognized authentication mechanism %q for transport %s", mech, transportName)
}
// No mutually supported algorithm.
return nil, nil
}
}
clientctx, clientcancel := context.WithTimeout(context.Background(), 60*time.Second)