Potential header overwriting through header extensions Webklex#35

Author: Webklex

CHANGELOG.md

@@ -7,13 +7,15 @@ Updates should follow the [Keep a CHANGELOG](http://keepachangelog.com/) princip
 ## [UNRELEASED]
 ### Fixed
 - Text/Html body fetched as attachment if subtype is null #34
+- Potential header overwriting through header extensions #35
 
 ### Added
 - NaN
 
 ### Affected Classes
 - [Message::class](src/Message.php)
 - [Part::class](src/Part.php)
+- [Header::class](src/Header.php)
 
 ### Breaking changes
 - NaN

src/Header.php

@@ -528,9 +528,15 @@ private function extractHeaderExtensions(){
                     foreach($extensions as $extension) {
                         if (($pos = strpos($extension, "=")) !== false){
                             $key = substr($extension, 0, $pos);
-                            $value = substr($extension, $pos + 1);
-                            $value = str_replace('"', "", $value);
-                            $this->attributes[trim(rtrim(strtolower($key)))] = trim(rtrim($value));
+                            $key = trim(rtrim(strtolower($key)));
+
+                            if (isset($this->attributes[$key]) === false) {
+                                $value = substr($extension, $pos + 1);
+                                $value = str_replace('"', "", $value);
+                                $value = trim(rtrim($value));
+
+                                $this->attributes[$key] = $value;
+                            }
                         }
                     }
                 }