Fix issue when the connection was remotely closed

src/modules/smtp/private.go

@@ -0,0 +1,36 @@
+package smtp
+
+import (
+	"GoMapEnum/src/utils"
+
+	smtp "github.com/nodauf/net-smtp"
+)
+
+func (options *Options) prepareOneConnection(client *smtp.Client) error {
+
+	mailFrom := utils.RandomString(6) + "@" + options.Domain
+	err := client.Mail(mailFrom)
+	if err != nil {
+		//options.Log.Error("Mail From command failed with email:  " + mailFrom + " and error " + err.Error())
+		return err
+	}
+	options.Log.Debug("One connection has been successfully prepared")
+
+	return nil
+}
+
+func (options *Options) createNewConnection() *smtp.Client {
+	client, err := smtp.Dial(options.Target + ":25")
+	if err != nil {
+		options.Log.Error("Failed to establish a connection " + err.Error())
+		return nil
+	}
+
+	hello := utils.RandomString(6)
+	err = client.Hello(hello)
+	if err != nil {
+		options.Log.Error("helo command failed with helo " + hello + " and error " + err.Error())
+		return nil
+	}
+	return client
+}

src/modules/smtp/struct.go

@@ -13,8 +13,9 @@ type Options struct {
 	Mode   string
 	utils.BaseOptions
 
-	all             bool
-	connectionsPool chan *smtp.Client
+	all               bool
+	connectionsPool   chan *smtp.Client
+	expnNotRecognized bool
 }
 
 func (options *Options) GetBaseOptions() *utils.BaseOptions {

src/modules/smtp/userEnum.go

@@ -1,8 +1,6 @@
 package smtp
 
 import (
-	"GoMapEnum/src/utils"
-	"fmt"
 	"net"
 	"reflect"
 	"strconv"
@@ -32,27 +30,27 @@ func PrepareSMTPConnections(optionsInterface *interface{}) {
 	}
 	options.Log.Debug("Preparing a pool of " + strconv.Itoa(nbConnectionsRequired) + " connections")
 	for i := 1; i <= nbConnectionsRequired; i++ {
-		client, err := smtp.Dial(options.Target + ":25")
-		if err != nil {
-			options.Log.Error("Failed to establish a connection " + err.Error())
-			continue
-		}
-		err = client.Hello(utils.RandomString(6))
-		if err != nil {
-			fmt.Println("hello" + err.Error())
-		}
-		err = client.Mail(utils.RandomString(6) + "@" + options.Domain)
-		if err != nil {
-			fmt.Println("mail" + err.Error())
+		client := options.createNewConnection()
+		if client != nil {
+			options.connectionsPool <- client
 		}
-		options.connectionsPool <- client
 	}
 }
 
 func UserEnum(optionsInterface *interface{}, username string) bool {
 	options := (*optionsInterface).(*Options)
 	valid := false
 	smtpConnection := <-options.connectionsPool
+	smtpConnection.Reset()
+	err := options.prepareOneConnection(smtpConnection)
+	if err != nil && strings.Contains(err.Error(), "connection reset by peer") {
+		options.Log.Debug("Connection reset. Generating new one")
+		smtpConnection = options.createNewConnection()
+		err = options.prepareOneConnection(smtpConnection)
+	}
+	if err != nil {
+		options.Log.Fatal("Failed to prepare a connection. " + err.Error())
+	}
 	switch strings.ToLower(options.Mode) {
 	case "rcpt":
 		err := smtpConnection.Rcpt(username)
@@ -61,6 +59,11 @@ func UserEnum(optionsInterface *interface{}, username string) bool {
 			valid = true
 		} else {
 			options.Log.Debug(username + " => " + err.Error())
+			if strings.Contains(err.Error(), "connection reset by peer") {
+				smtpConnection.Close()
+				options.createNewConnection()
+				return UserEnum(optionsInterface, username)
+			}
 			options.Log.Fail(username)
 		}
 	case "vrfy":
@@ -70,6 +73,11 @@ func UserEnum(optionsInterface *interface{}, username string) bool {
 			valid = true
 		} else {
 			options.Log.Debug(username + " => " + err.Error())
+			if strings.Contains(err.Error(), "connection reset by peer") {
+				smtpConnection.Close()
+				options.createNewConnection()
+				return UserEnum(optionsInterface, username)
+			}
 			options.Log.Fail(username)
 		}
 	case "expn":
@@ -80,12 +88,20 @@ func UserEnum(optionsInterface *interface{}, username string) bool {
 		} else {
 			code := strings.Split(err.Error(), " ")[0]
 			options.Log.Debug(username + " => " + err.Error())
+			if strings.Contains(err.Error(), "connection reset by peer") {
+				smtpConnection.Close()
+				options.createNewConnection()
+				return UserEnum(optionsInterface, username)
+			}
 			options.Log.Fail(username)
 			// If the command is not implemented no need to pursue
 			if code == "502" && !options.all {
 				CloseSMTPConnections(optionsInterface)
 				options.Log.Fatal("The command EXPN is not implemented. No need to pursue using this method.")
 			}
+			if code == "502" && options.all {
+				options.expnNotRecognized = true
+			}
 		}
 	case "", "all":
 
@@ -111,15 +127,16 @@ func UserEnum(optionsInterface *interface{}, username string) bool {
 			return true
 		}
 		// EXPN
-		options.Log.Debug("Enumerate with EXPN")
-		optionsCopy.Mode = "expn"
-		newOptionsInterface = reflect.ValueOf(&optionsCopy).Interface()
-		valid = UserEnum(&newOptionsInterface, username)
+		if !options.expnNotRecognized {
+			options.Log.Debug("Enumerate with EXPN")
+			optionsCopy.Mode = "expn"
+			newOptionsInterface = reflect.ValueOf(&optionsCopy).Interface()
+			valid = UserEnum(&newOptionsInterface, username)
+		}
 		return valid
 	default:
 		options.Log.Fatal("Unrecognised mode: " + options.Mode + ". Only RCPT, VRFY and EXPN are supported.")
 	}
-
 	options.connectionsPool <- smtpConnection
 	return valid
 }