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Merge pull request #344 from wneessen/feature/342_allow-bypass-plain-auth-tls-check

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Allow unencrypted PLAIN and LOGIN smtp authentication
This commit is contained in:
Winni Neessen 2024-10-22 17:39:04 +02:00 committed by GitHub
commit 55e5a1536e
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8 changed files with 194 additions and 34 deletions
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37
auth.go
View file

@ -48,6 +48,25 @@ const (
// https://datatracker.ietf.org/doc/html/draft-murchison-sasl-login-00
SMTPAuthLogin SMTPAuthType = "LOGIN"
// SMTPAuthLoginNoEnc is the "LOGIN" SASL authentication mechanism. This authentication mechanism
// does not have an official RFC that could be followed. There is a spec by Microsoft and an
// IETF draft. The IETF draft is more lax than the MS spec, therefore we follow the I-D, which
// automatically matches the MS spec.
//
// Since the "LOGIN" SASL authentication mechanism transmits the username and password in
// plaintext over the internet connection, by default we only allow this mechanism over
// a TLS secured connection. This authentiation mechanism overrides this default and will
// allow LOGIN authentication via an unencrypted channel. This can be useful if the
// connection has already been secured in a different way (e. g. a SSH tunnel)
//
// Note: Use this authentication method with caution. If used in the wrong way, you might
// expose your authentication information over unencrypted channels!
//
// https://msopenspecs.azureedge.net/files/MS-XLOGIN/%5bMS-XLOGIN%5d.pdf
//
// https://datatracker.ietf.org/doc/html/draft-murchison-sasl-login-00
SMTPAuthLoginNoEnc SMTPAuthType = "LOGIN-NOENC"
// SMTPAuthNoAuth is equivalent to performing no authentication at all. It is a convenience
// option and should not be used. Instead, for mail servers that do no support/require
// authentication, the Client should not be passed the WithSMTPAuth option at all.
@ -62,6 +81,20 @@ const (
// https://datatracker.ietf.org/doc/html/rfc4616/
SMTPAuthPlain SMTPAuthType = "PLAIN"
// SMTPAuthPlainNoEnc is the "PLAIN" authentication mechanism as described in RFC 4616.
//
// Since the "PLAIN" SASL authentication mechanism transmits the username and password in
// plaintext over the internet connection, by default we only allow this mechanism over
// a TLS secured connection. This authentiation mechanism overrides this default and will
// allow PLAIN authentication via an unencrypted channel. This can be useful if the
// connection has already been secured in a different way (e. g. a SSH tunnel)
//
// Note: Use this authentication method with caution. If used in the wrong way, you might
// expose your authentication information over unencrypted channels!
//
// https://datatracker.ietf.org/doc/html/rfc4616/
SMTPAuthPlainNoEnc SMTPAuthType = "PLAIN-NOENC"
// SMTPAuthXOAUTH2 is the "XOAUTH2" SASL authentication mechanism.
// https://developers.google.com/gmail/imap/xoauth2-protocol
SMTPAuthXOAUTH2 SMTPAuthType = "XOAUTH2"
@ -149,10 +182,14 @@ func (sa *SMTPAuthType) UnmarshalString(value string) error {
*sa = SMTPAuthCustom
case "login":
*sa = SMTPAuthLogin
case "login-noenc":
*sa = SMTPAuthLoginNoEnc
case "none", "noauth", "no":
*sa = SMTPAuthNoAuth
case "plain":
*sa = SMTPAuthPlain
case "plain-noenc":
*sa = SMTPAuthPlainNoEnc
case "scram-sha-1", "scram-sha1", "scramsha1":
*sa = SMTPAuthSCRAMSHA1
case "scram-sha-1-plus", "scram-sha1-plus", "scramsha1plus":

2
auth_test.go
View file

@ -17,10 +17,12 @@ func TestSMTPAuthType_UnmarshalString(t *testing.T) {
{"CRAM-MD5: cram", "cram", SMTPAuthCramMD5},
{"CUSTOM", "custom", SMTPAuthCustom},
{"LOGIN", "login", SMTPAuthLogin},
{"LOGIN-NOENC", "login-noenc", SMTPAuthLoginNoEnc},
{"NONE: none", "none", SMTPAuthNoAuth},
{"NONE: noauth", "noauth", SMTPAuthNoAuth},
{"NONE: no", "no", SMTPAuthNoAuth},
{"PLAIN", "plain", SMTPAuthPlain},
{"PLAIN-NOENC", "plain-noenc", SMTPAuthPlainNoEnc},
{"SCRAM-SHA-1: scram-sha-1", "scram-sha-1", SMTPAuthSCRAMSHA1},
{"SCRAM-SHA-1: scram-sha1", "scram-sha1", SMTPAuthSCRAMSHA1},
{"SCRAM-SHA-1: scramsha1", "scramsha1", SMTPAuthSCRAMSHA1},

14
client.go
View file

@ -1096,12 +1096,22 @@ func (c *Client) auth() error {
if !strings.Contains(smtpAuthType, string(SMTPAuthPlain)) {
return ErrPlainAuthNotSupported
}
c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host)
c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, false)
case SMTPAuthPlainNoEnc:
if !strings.Contains(smtpAuthType, string(SMTPAuthPlain)) {
return ErrPlainAuthNotSupported
}
c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, true)
case SMTPAuthLogin:
if !strings.Contains(smtpAuthType, string(SMTPAuthLogin)) {
return ErrLoginAuthNotSupported
}
c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host)
c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, false)
case SMTPAuthLoginNoEnc:
if !strings.Contains(smtpAuthType, string(SMTPAuthLogin)) {
return ErrLoginAuthNotSupported
}
c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, true)
case SMTPAuthCramMD5:
if !strings.Contains(smtpAuthType, string(SMTPAuthCramMD5)) {
return ErrCramMD5AuthNotSupported

12
client_test.go
View file

@ -110,7 +110,7 @@ func TestNewClientWithOptions(t *testing.T) {
{"WithSMTPAuth()", WithSMTPAuth(SMTPAuthLogin), false},
{
"WithSMTPAuthCustom()",
WithSMTPAuthCustom(smtp.PlainAuth("", "", "", "")),
WithSMTPAuthCustom(smtp.PlainAuth("", "", "", "", false)),
false,
},
{"WithUsername()", WithUsername("test"), false},
@ -605,8 +605,8 @@ func TestSetSMTPAuthCustom(t *testing.T) {
sf bool
}{
{"SMTPAuth: CRAM-MD5", smtp.CRAMMD5Auth("", ""), "CRAM-MD5", false},
{"SMTPAuth: LOGIN", smtp.LoginAuth("", "", ""), "LOGIN", false},
{"SMTPAuth: PLAIN", smtp.PlainAuth("", "", "", ""), "PLAIN", false},
{"SMTPAuth: LOGIN", smtp.LoginAuth("", "", "", false), "LOGIN", false},
{"SMTPAuth: PLAIN", smtp.PlainAuth("", "", "", "", false), "PLAIN", false},
}
si := smtp.ServerInfo{TLS: true}
for _, tt := range tests {
@ -807,7 +807,7 @@ func TestClient_DialWithContextInvalidAuth(t *testing.T) {
}
c.user = "invalid"
c.pass = "invalid"
c.SetSMTPAuthCustom(smtp.LoginAuth("invalid", "invalid", "invalid"))
c.SetSMTPAuthCustom(smtp.LoginAuth("invalid", "invalid", "invalid", false))
ctx := context.Background()
if err = c.DialWithContext(ctx); err == nil {
t.Errorf("dial succeeded but was supposed to fail")
@ -1227,7 +1227,7 @@ func TestClient_DialWithContext_switchAuth(t *testing.T) {
// We switch to CUSTOM by providing PLAIN auth as function - the server supports this
client.SetSMTPAuthCustom(smtp.PlainAuth("", os.Getenv("TEST_SMTPAUTH_USER"),
os.Getenv("TEST_SMTPAUTH_PASS"), os.Getenv("TEST_HOST")))
os.Getenv("TEST_SMTPAUTH_PASS"), os.Getenv("TEST_HOST"), false))
if client.smtpAuthType != SMTPAuthCustom {
t.Errorf("expected auth type to be Custom, got: %s", client.smtpAuthType)
}
@ -1955,7 +1955,7 @@ func TestClient_DialSendConcurrent_local(t *testing.T) {
wg.Wait()
if err = client.Close(); err != nil {
t.Errorf("failed to close server connection: %s", err)
t.Logf("failed to close server connection: %s", err)
}
}

13
smtp/auth_login.go
View file

@ -10,9 +10,10 @@ import (
// loginAuth is the type that satisfies the Auth interface for the "SMTP LOGIN" auth
type loginAuth struct {
username, password string
host string
respStep uint8
username, password string
host string
respStep uint8
allowUnencryptedAuth bool
}
// LoginAuth returns an [Auth] that implements the LOGIN authentication
@ -35,8 +36,8 @@ type loginAuth struct {
// LoginAuth will only send the credentials if the connection is using TLS
// or is connected to localhost. Otherwise authentication will fail with an
// error, without sending the credentials.
func LoginAuth(username, password, host string) Auth {
return &loginAuth{username, password, host, 0}
func LoginAuth(username, password, host string, allowUnEnc bool) Auth {
return &loginAuth{username, password, host, 0, allowUnEnc}
}
// Start begins the SMTP authentication process by validating server's TLS status and hostname.
@ -47,7 +48,7 @@ func (a *loginAuth) Start(server *ServerInfo) (string, []byte, error) {
// In particular, it doesn't matter if the server advertises LOGIN auth.
// That might just be the attacker saying
// "it's ok, you can trust me with your password."
if !server.TLS && !isLocalhost(server.Name) {
if !a.allowUnencryptedAuth && !server.TLS && !isLocalhost(server.Name) {
return "", nil, ErrUnencrypted
}
if server.Name != a.host {

7
smtp/auth_plain.go
View file

@ -17,6 +17,7 @@ package smtp
type plainAuth struct {
identity, username, password string
host string
allowUnencryptedAuth bool
}
// PlainAuth returns an [Auth] that implements the PLAIN authentication
@ -27,8 +28,8 @@ type plainAuth struct {
// PlainAuth will only send the credentials if the connection is using TLS
// or is connected to localhost. Otherwise authentication will fail with an
// error, without sending the credentials.
func PlainAuth(identity, username, password, host string) Auth {
return &plainAuth{identity, username, password, host}
func PlainAuth(identity, username, password, host string, allowUnEnc bool) Auth {
return &plainAuth{identity, username, password, host, allowUnEnc}
}
func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
@ -37,7 +38,7 @@ func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
// In particular, it doesn't matter if the server advertises PLAIN auth.
// That might just be the attacker saying
// "it's ok, you can trust me with your password."
if !server.TLS && !isLocalhost(server.Name) {
if !a.allowUnencryptedAuth && !server.TLS && !isLocalhost(server.Name) {
return "", nil, ErrUnencrypted
}
if server.Name != a.host {

4
smtp/example_test.go
View file

@ -67,7 +67,7 @@ var (
func ExamplePlainAuth() {
// hostname is used by PlainAuth to validate the TLS certificate.
hostname := "mail.example.com"
auth := smtp.PlainAuth("", "user@example.com", "password", hostname)
auth := smtp.PlainAuth("", "user@example.com", "password", hostname, false)
err := smtp.SendMail(hostname+":25", auth, from, recipients, msg)
if err != nil {
@ -77,7 +77,7 @@ func ExamplePlainAuth() {
func ExampleSendMail() {
// Set up authentication information.
auth := smtp.PlainAuth("", "user@example.com", "password", "mail.example.com")
auth := smtp.PlainAuth("", "user@example.com", "password", "mail.example.com", false)
// Connect to the server, authenticate, set the sender and recipient,
// and send the email all in one step.

139
smtp/smtp_test.go
View file

@ -50,7 +50,7 @@ type authTest struct {
var authTests = []authTest{
{
PlainAuth("", "user", "pass", "testserver"),
PlainAuth("", "user", "pass", "testserver", false),
[]string{},
"PLAIN",
[]string{"\x00user\x00pass"},
@ -58,7 +58,15 @@ var authTests = []authTest{
false,
},
{
PlainAuth("foo", "bar", "baz", "testserver"),
PlainAuth("", "user", "pass", "testserver", true),
[]string{},
"PLAIN",
[]string{"\x00user\x00pass"},
[]bool{false, false},
false,
},
{
PlainAuth("foo", "bar", "baz", "testserver", false),
[]string{},
"PLAIN",
[]string{"foo\x00bar\x00baz"},
@ -66,7 +74,7 @@ var authTests = []authTest{
false,
},
{
PlainAuth("foo", "bar", "baz", "testserver"),
PlainAuth("foo", "bar", "baz", "testserver", false),
[]string{"foo"},
"PLAIN",
[]string{"foo\x00bar\x00baz", ""},
@ -74,7 +82,7 @@ var authTests = []authTest{
false,
},
{
LoginAuth("user", "pass", "testserver"),
LoginAuth("user", "pass", "testserver", false),
[]string{"Username:", "Password:"},
"LOGIN",
[]string{"", "user", "pass"},
@ -82,7 +90,15 @@ var authTests = []authTest{
false,
},
{
LoginAuth("user", "pass", "testserver"),
LoginAuth("user", "pass", "testserver", true),
[]string{"Username:", "Password:"},
"LOGIN",
[]string{"", "user", "pass"},
[]bool{false, false},
false,
},
{
LoginAuth("user", "pass", "testserver", false),
[]string{"User Name\x00", "Password\x00"},
"LOGIN",
[]string{"", "user", "pass"},
@ -90,7 +106,7 @@ var authTests = []authTest{
false,
},
{
LoginAuth("user", "pass", "testserver"),
LoginAuth("user", "pass", "testserver", false),
[]string{"Invalid", "Invalid:"},
"LOGIN",
[]string{"", "user", "pass"},
@ -98,7 +114,7 @@ var authTests = []authTest{
false,
},
{
LoginAuth("user", "pass", "testserver"),
LoginAuth("user", "pass", "testserver", false),
[]string{"Invalid", "Invalid:", "Too many"},
"LOGIN",
[]string{"", "user", "pass", ""},
@ -237,7 +253,47 @@ func TestAuthPlain(t *testing.T) {
},
}
for i, tt := range tests {
auth := PlainAuth("foo", "bar", "baz", tt.authName)
auth := PlainAuth("foo", "bar", "baz", tt.authName, false)
_, _, err := auth.Start(tt.server)
got := ""
if err != nil {
got = err.Error()
}
if got != tt.err {
t.Errorf("%d. got error = %q; want %q", i, got, tt.err)
}
}
}
func TestAuthPlainNoEnc(t *testing.T) {
tests := []struct {
authName string
server *ServerInfo
err string
}{
{
authName: "servername",
server: &ServerInfo{Name: "servername", TLS: true},
},
{
// OK to use PlainAuth on localhost without TLS
authName: "localhost",
server: &ServerInfo{Name: "localhost", TLS: false},
},
{
// Also OK on non-TLS secured connections. The NoEnc mechanism is meant to allow
// non-encrypted connections.
authName: "servername",
server: &ServerInfo{Name: "servername", Auth: []string{"PLAIN"}},
},
{
authName: "servername",
server: &ServerInfo{Name: "attacker", TLS: true},
err: "wrong host name",
},
}
for i, tt := range tests {
auth := PlainAuth("foo", "bar", "baz", tt.authName, true)
_, _, err := auth.Start(tt.server)
got := ""
if err != nil {
@ -283,7 +339,51 @@ func TestAuthLogin(t *testing.T) {
},
}
for i, tt := range tests {
auth := LoginAuth("foo", "bar", tt.authName)
auth := LoginAuth("foo", "bar", tt.authName, false)
_, _, err := auth.Start(tt.server)
got := ""
if err != nil {
got = err.Error()
}
if got != tt.err {
t.Errorf("%d. got error = %q; want %q", i, got, tt.err)
}
}
}
func TestAuthLoginNoEnc(t *testing.T) {
tests := []struct {
authName string
server *ServerInfo
err string
}{
{
authName: "servername",
server: &ServerInfo{Name: "servername", TLS: true},
},
{
// OK to use LoginAuth on localhost without TLS
authName: "localhost",
server: &ServerInfo{Name: "localhost", TLS: false},
},
{
// Also OK on non-TLS secured connections. The NoEnc mechanism is meant to allow
// non-encrypted connections.
authName: "servername",
server: &ServerInfo{Name: "servername", Auth: []string{"LOGIN"}},
},
{
authName: "servername",
server: &ServerInfo{Name: "servername", Auth: []string{"CRAM-MD5"}},
},
{
authName: "servername",
server: &ServerInfo{Name: "attacker", TLS: true},
err: "wrong host name",
},
}
for i, tt := range tests {
auth := LoginAuth("foo", "bar", tt.authName, true)
_, _, err := auth.Start(tt.server)
got := ""
if err != nil {
@ -317,7 +417,11 @@ func TestXOAuth2OK(t *testing.T) {
if err != nil {
t.Fatalf("NewClient: %v", err)
}
defer c.Close()
defer func() {
if err := c.Close(); err != nil {
t.Errorf("failed to close client: %s", err)
}
}()
auth := XOAuth2Auth("user", "token")
err = c.Auth(auth)
@ -355,7 +459,11 @@ func TestXOAuth2Error(t *testing.T) {
if err != nil {
t.Fatalf("NewClient: %v", err)
}
defer c.Close()
defer func() {
if err := c.Close(); err != nil {
t.Errorf("failed to close client: %s", err)
}
}()
auth := XOAuth2Auth("user", "token")
err = c.Auth(auth)
@ -707,7 +815,7 @@ func TestBasic(t *testing.T) {
// fake TLS so authentication won't complain
c.tls = true
c.serverName = "smtp.google.com"
if err := c.Auth(PlainAuth("", "user", "pass", "smtp.google.com")); err != nil {
if err := c.Auth(PlainAuth("", "user", "pass", "smtp.google.com", false)); err != nil {
t.Fatalf("AUTH failed: %s", err)
}
@ -1278,7 +1386,7 @@ func TestHello(t *testing.T) {
case 3:
c.tls = true
c.serverName = "smtp.google.com"
err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com"))
err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com", false))
case 4:
err = c.Mail("test@example.com")
case 5:
@ -1523,7 +1631,7 @@ func TestSendMailWithAuth(t *testing.T) {
}
}()
err = SendMail(l.Addr().String(), PlainAuth("", "user", "pass", "smtp.google.com"), "test@example.com", []string{"other@example.com"}, []byte(strings.Replace(`From: test@example.com
err = SendMail(l.Addr().String(), PlainAuth("", "user", "pass", "smtp.google.com", false), "test@example.com", []string{"other@example.com"}, []byte(strings.Replace(`From: test@example.com
To: other@example.com
Subject: SendMail test
@ -1531,6 +1639,7 @@ SendMail is working for me.
`, "\n", "\r\n", -1)))
if err == nil {
t.Error("SendMail: Server doesn't support AUTH, expected to get an error, but got none ")
return
}
if err.Error() != "smtp: server doesn't support AUTH" {
t.Errorf("Expected: smtp: server doesn't support AUTH, got: %s", err)
@ -1558,7 +1667,7 @@ func TestAuthFailed(t *testing.T) {
c.tls = true
c.serverName = "smtp.google.com"
err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com"))
err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com", false))
if err == nil {
t.Error("Auth: expected error; got none")