diff --git a/functions/functions.php b/functions/functions.php
index 064334f..878aca5 100644
--- a/functions/functions.php
+++ b/functions/functions.php
@@ -44,7 +44,7 @@ function lang_getfrombrowser(array $allowed_languages, string $default_language,
 
         // Alle Infos über diese Sprache rausholen
         // phpcs:disable Generic.Strings.UnnecessaryStringConcat
-        $res = preg_match('/^([a-z]{1,8}(?:-[a-z]{1,8})*)' . '(?:;\s*q=(0(?:\.[0-9]{1,3})?|1(?:\.0{1,3})?))?$/i', $accepted_language, $matches);
+        $res = preg_match('/^([a-z]{1,8}(?:-[a-z]{1,8})*)(?:;\s*q=(0(?:\.[0-9]{1,3})?|1(?:\.0{1,3})?))?$/i', $accepted_language, $matches);
         // phpcs:enable
 
         // war die Syntax gültig?
@@ -66,9 +66,7 @@ function lang_getfrombrowser(array $allowed_languages, string $default_language,
         }
 
         // Bis der Sprachcode leer ist...
-        // phpcs:disable Squiz.PHP.DisallowSizeFunctionsInLoops
-        while (count($lang_code)) {
-            // phpcs:enable
+        while (!empty($lang_code)) {
             // mal sehen, ob der Sprachcode angeboten wird
             if (in_array(strtolower(join('-', $lang_code)), $allowed_languages)) {
                 // Qualität anschauen
@@ -252,3 +250,39 @@ function identical_values(array $arrayA, array $arrayB):bool {
     return $arrayA == $arrayB;
 
 }
+
+/**
+ * Function for retrieving the anti-csrf token or generating it if need be.
+ *
+ * @return string
+ */
+function getAntiCsrfToken():string {
+
+    if (empty($_SESSION['anti-csrf-token'])) {
+        $_SESSION['anti-csrf-token'] = bin2hex(random_bytes(32));
+    }
+
+    return $_SESSION['anti-csrf-token'];
+
+}
+
+/**
+ * Function for validating anti-csrf tokens. Each anti-csrf token is removed
+ * after use.
+ *
+ * @return boolean
+ */
+function validateAntiCsrfToken():bool {
+
+    $validity = false;
+    if (!empty($_POST['anti-csrf-token'])
+        && !empty($_SESSION['anti-csrf-token'])
+        && hash_equals($_SESSION['anti-csrf-token'], $_POST['anti-csrf-token']) === true
+    ) {
+        $validity = true;
+    }
+    $_SESSION['anti-csrf-token'] = null; unset($_SESSION['anti-csrf-token']);
+
+    return $validity;
+
+}
diff --git a/index.php b/index.php
index da6d05f..23837ad 100644
--- a/index.php
+++ b/index.php
@@ -43,6 +43,7 @@ echo '
 
 <div class="uploader">
     <form enctype="multipart/form-data" action="upload.php" method="POST">
+        <input type="hidden" id="csrf-token" name="csrf-token" aria-label="Anti-CSRF Token" value="' . htmlspecialchars(getAntiCsrfToken()) . '" />
         <label for="fileToUpload">' . $csvxml_overview['select_csv_file_for_upload'] . '</label>
         <input name="uploaded" type="file" accept=".csv" id="fileToUpload" required />
         <button type="submit">' . $csvxml_overview['upload'] . '</button>
diff --git a/upload.php b/upload.php
index c66cb4d..0dbd633 100644
--- a/upload.php
+++ b/upload.php
@@ -3,8 +3,12 @@ declare(strict_types = 1);
 require_once __DIR__ . "/functions/functions.php";
 
 $target = "csv/";
-$target .= basename( $_FILES['uploaded']['name']);
-$targetpart = basename( $_FILES['uploaded']['name']);
+$target .= basename($_FILES['uploaded']['name']);
+$targetpart = basename($_FILES['uploaded']['name']);
+
+if (validateAntiCsrfToken() === false) {
+    throw new WrongCsrfTokenException();
+}
 
 //This is our size condition
 if ($uploaded_size > 40000000) {