diff --git a/includes/database.mysqli.inc b/includes/database.mysqli.inc
index b373730eabc..039f011c909 100644
--- a/includes/database.mysqli.inc
+++ b/includes/database.mysqli.inc
@@ -40,7 +40,6 @@ function db_status_report($phase) {
 /**
  * Returns the version of the database server currently in use.
  *
- * @return Database server version
  */
 function db_version() {
   global $active_db;
@@ -333,7 +332,7 @@ function db_decode_blob($data) {
  */
 function db_escape_string($text) {
   global $active_db;
-  return mysqli_real_escape_string($active_db, $text);
+  return mysqli_real_escape_string($active_db, $text ?? '');
 }
 
 /**
diff --git a/includes/form.inc b/includes/form.inc
index 53ae400acea..7bcb03de518 100644
--- a/includes/form.inc
+++ b/includes/form.inc
@@ -476,7 +476,7 @@ function drupal_process_form($form_id, &$form, &$form_state) {
       // possibly ending execution. We make sure we do not react to the batch
       // that is already being processed (if a batch operation performs a
       // drupal_execute).
-      if ($batch =& batch_get() && !isset($batch['current_set'])) {
+      if ($batch = batch_get() && !isset($batch['current_set'])) {
         // The batch uses its own copies of $form and $form_state for
         // late execution of submit handers and post-batch redirection.
         $batch['form'] = $form;
@@ -1379,7 +1379,7 @@ function form_type_textfield_value($form, $edit = FALSE) {
   if ($edit !== FALSE) {
     // Equate $edit to the form value to ensure it's marked for
     // validation.
-    return str_replace(array("\r", "\n"), '', $edit);
+    return str_replace(array("\r", "\n"), '', $edit ?? '');
   }
 }
 
diff --git a/includes/menu.inc b/includes/menu.inc
index 5b0a97c5b55..c869978e30b 100644
--- a/includes/menu.inc
+++ b/includes/menu.inc
@@ -576,7 +576,9 @@ function _menu_translate(&$router_item, $map, $to_arg = FALSE) {
   $link_map = explode('/', $router_item['path']);
   for ($i = 0; $i < $router_item['number_parts']; $i++) {
     if ($link_map[$i] == '%') {
-      $link_map[$i] = $path_map[$i];
+      if (array_key_exists($i, $path_map)) {
+        $link_map[$i] = $path_map[$i];
+      }
     }
   }
   $router_item['href'] = implode('/', $link_map);
diff --git a/install.php b/install.php
index b2764100ae6..dbbaf3fdc10 100644
--- a/install.php
+++ b/install.php
@@ -397,7 +397,7 @@ function _install_settings_form_validate($db_prefix, $db_type, $db_user, $db_pas
     $function = 'drupal_test_'. $db_type;
     if (!$function($db_url, $success)) {
       if (isset($success['CONNECT'])) {
-        form_set_error('db_type', st('In order for Drupal to work, and to continue with the installation process, you must resolve all permission issues reported above. We were able to verify that we have permission for the following commands: %commands. For more help with configuring your database server, see the <a href="http://drupal.org/node/258">Installation and upgrading handbook</a>. If you are unsure what any of this means you should probably contact your hosting provider.', array('%commands' => implode($success, ', '))));
+        form_set_error('db_type', st('In order for Drupal to work, and to continue with the installation process, you must resolve all permission issues reported above. We were able to verify that we have permission for the following commands: %commands. For more help with configuring your database server, see the <a href="http://drupal.org/node/258">Installation and upgrading handbook</a>. If you are unsure what any of this means you should probably contact your hosting provider.', array('%commands' => implode(', ', $success))));
       }
       else {
         form_set_error('db_type', '');
diff --git a/modules/comment/comment.module b/modules/comment/comment.module
index 34c6deb117b..19be88f6f6d 100644
--- a/modules/comment/comment.module
+++ b/modules/comment/comment.module
@@ -760,6 +760,8 @@ function comment_save($edit) {
           $edit['name'] = $user->name;
         }
 
+        $edit['format'] = $edit['format'] ?? FILTER_FORMAT_DEFAULT;
+
         db_query("INSERT INTO {comments} (nid, pid, uid, subject, comment, format, hostname, timestamp, status, thread, name, mail, homepage) VALUES (%d, %d, %d, '%s', '%s', %d, '%s', %d, %d, '%s', '%s', '%s', '%s')", $edit['nid'], $edit['pid'], $edit['uid'], $edit['subject'], $edit['comment'], $edit['format'], ip_address(), $edit['timestamp'], $edit['status'], $thread, $edit['name'], $edit['mail'], $edit['homepage']);
         $edit['cid'] = db_last_insert_id('comments', 'cid');
 
diff --git a/modules/node/node.module b/modules/node/node.module
index 4cc6bdfb715..f9236079cad 100644
--- a/modules/node/node.module
+++ b/modules/node/node.module
@@ -447,13 +447,13 @@ function node_get_types($op = 'types', $node = NULL, $reset = FALSE) {
     case 'types':
       return $_node_types;
     case 'type':
-      return isset($_node_types[$type]) ? $_node_types[$type] : FALSE;
+      return isset($type) && isset($_node_types[$type]) ? $_node_types[$type] : FALSE;
     case 'module':
-      return isset($_node_types[$type]->module) ? $_node_types[$type]->module : FALSE;
+      return isset($type) && isset($_node_types[$type]->module) ? $_node_types[$type]->module : FALSE;
     case 'names':
       return $_node_names;
     case 'name':
-      return isset($_node_names[$type]) ? $_node_names[$type] : FALSE;
+      return isset($type) && isset($_node_names[$type]) ? $_node_names[$type] : FALSE;
   }
 }
 
@@ -1048,13 +1048,13 @@ function node_prepare($node, $teaser = FALSE) {
   // First we'll overwrite the existing node teaser and body with
   // the filtered copies! Then, we'll stick those into the content
   // array and set the read more flag if appropriate.
-  $node->readmore = $node->teaser != $node->body;
+  $node->readmore = property_exists($node, 'teaser') && $node->teaser != $node->body;
 
   if ($teaser == FALSE) {
     $node->body = check_markup($node->body, $node->format, FALSE);
   }
   else {
-    $node->teaser = check_markup($node->teaser, $node->format, FALSE);
+    $node->teaser = check_markup(($node->teaser ?? ''), $node->format, FALSE);
   }
 
   $node->content['body'] = array(
diff --git a/modules/system/system.admin.inc b/modules/system/system.admin.inc
index 315390cf21b..fa715990df8 100644
--- a/modules/system/system.admin.inc
+++ b/modules/system/system.admin.inc
@@ -1759,7 +1759,7 @@ function system_run_cron() {
  * Menu callback: return information about PHP.
  */
 function system_php() {
-  phpinfo();
+  phpinfo(~ (INFO_VARIABLES | INFO_ENVIRONMENT));
   exit();
 }
 
diff --git a/modules/system/system.module b/modules/system/system.module
index 77824466bb7..25cac7eba44 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -8,7 +8,7 @@
 /**
  * The current system version.
  */
-define('VERSION', '6.60');
+define('VERSION', '6.61');
 
 /**
  * Core API compatibility.
@@ -18,7 +18,7 @@ define('DRUPAL_CORE_COMPATIBILITY', '6.x');
 /**
  * Minimum supported version of PHP.
  */
-define('DRUPAL_MINIMUM_PHP',    '4.3.5');
+define('DRUPAL_MINIMUM_PHP',    '8.1');
 
 /**
  * Minimum recommended value of PHP memory_limit.
diff --git a/modules/user/user.module b/modules/user/user.module
index 5ff9a35a361..b7a8fe63a56 100644
--- a/modules/user/user.module
+++ b/modules/user/user.module
@@ -1533,7 +1533,7 @@ function user_edit_form(&$form_state, $uid, $edit, $register = FALSE) {
   if ($register || ($GLOBALS['user']->uid == $uid && user_access('change own username')) || $admin) {
     $form['account']['name'] = array('#type' => 'textfield',
       '#title' => t('Username'),
-      '#default_value' => $edit['name'],
+      '#default_value' => ($edit['name'] ?? ''),
       '#maxlength' => USERNAME_MAX_LENGTH,
       '#description' => t('Spaces are allowed; punctuation is not allowed except for periods, hyphens, and underscores.'),
       '#required' => TRUE,
@@ -1541,7 +1541,7 @@ function user_edit_form(&$form_state, $uid, $edit, $register = FALSE) {
   }
   $form['account']['mail'] = array('#type' => 'textfield',
     '#title' => t('E-mail address'),
-    '#default_value' => $edit['mail'],
+    '#default_value' => ($edit['mail'] ?? ''),
     '#maxlength' => EMAIL_MAX_LENGTH,
     '#description' => t('A valid e-mail address. All e-mails from the system will be sent to this address. The e-mail address is not made public and will only be used if you wish to receive a new password or wish to receive certain news or notifications by e-mail.'),
     '#required' => TRUE,
diff --git a/update.php b/update.php
index 2ac80decd3e..378c1ab3473 100644
--- a/update.php
+++ b/update.php
@@ -313,7 +313,8 @@ function update_results_page() {
     $output = '<p>Updates were attempted. If you see no failures below, you may proceed happily to the <a href="'. base_path() .'?q=admin">administration pages</a>. Otherwise, you may need to update your database manually.'. $log_message .'</p>';
   }
   else {
-    list($module, $version) = array_pop(reset($_SESSION['updates_remaining']));
+    $updates_remaining = reset($_SESSION['updates_remaining']);
+    list($module, $version) = array_pop($updates_remaining);
     $output = '<p class="error">The update process was aborted prematurely while running <strong>update #'. $version .' in '. $module .'.module</strong>.'. $log_message;
     if (module_exists('dblog')) {
       $output .= ' You may need to check the <code>watchdog</code> database table manually.';