diff --git a/phpBB/includes/acp/acp_prune.php b/phpBB/includes/acp/acp_prune.php
index c5f7789de8..bffe993bc7 100644
--- a/phpBB/includes/acp/acp_prune.php
+++ b/phpBB/includes/acp/acp_prune.php
@@ -327,7 +327,7 @@ class acp_prune
 						'USERNAME'			=> $usernames[$user_id],
 						'USER_ID'           => $user_id,
 						'U_PROFILE'			=> get_username_string('profile', $user_id, $usernames[$user_id]),
-						'U_USER_ADMIN'		=> ($auth->acl_get('a_user')) ? append_sid("{$phpbb_admin_path}index.$phpEx", 'i=users&mode=overview&u=' . $user_id, true, $user->session_id) : '',
+						'U_USER_ADMIN'		=> ($auth->acl_get('a_user')) ? append_sid("{$phpbb_admin_path}index.$phpEx", 'i=users&mode=overview&u=' . $user_id) : '',
 					));
 				}
 
diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 80237fa901..9b303e4647 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -3716,7 +3716,7 @@ function page_header($page_title = '', $display_online_list = false, $item_id =
 	// Generate logged in/logged out status
 	if ($user->data['user_id'] != ANONYMOUS)
 	{
-		$u_login_logout = append_sid("{$phpbb_root_path}ucp.$phpEx", 'mode=logout', true, $user->session_id);
+		$u_login_logout = append_sid("{$phpbb_root_path}ucp.$phpEx", 'mode=logout');
 		$l_login_logout = $user->lang['LOGOUT'];
 	}
 	else
diff --git a/phpBB/includes/ucp/ucp_pm_compose.php b/phpBB/includes/ucp/ucp_pm_compose.php
index 7cb4c85916..8fe4c30179 100644
--- a/phpBB/includes/ucp/ucp_pm_compose.php
+++ b/phpBB/includes/ucp/ucp_pm_compose.php
@@ -542,7 +542,7 @@ function compose_pm($id, $mode, $action, $user_folders = array())
 	$message_parser->message = ($action == 'reply') ? '' : $message_text;
 	unset($message_text);
 
-	$s_action = append_sid("{$phpbb_root_path}ucp.$phpEx", "i=$id&mode=$mode&action=$action", true, $user->session_id);
+	$s_action = append_sid("{$phpbb_root_path}ucp.$phpEx", "i=$id&mode=$mode&action=$action");
 	$s_action .= (($folder_id) ? "&f=$folder_id" : '') . (($msg_id) ? "&p=$msg_id" : '');
 
 	// Delete triggered ?
diff --git a/phpBB/phpbb/controller/helper.php b/phpBB/phpbb/controller/helper.php
index 3262e6bbc4..e163894b4d 100644
--- a/phpBB/phpbb/controller/helper.php
+++ b/phpBB/phpbb/controller/helper.php
@@ -307,7 +307,7 @@ class helper
 				'TRANSLATION_INFO'		=> $this->language->is_set('TRANSLATION_INFO') ? $this->language->lang('TRANSLATION_INFO') : '',
 				'CREDIT_LINE'			=> $this->language->lang('POWERED_BY', '<a href="https://www.phpbb.com/">phpBB</a>&reg; Forum Software &copy; phpBB Limited'),
 
-				'U_ACP'					=> ($this->auth->acl_get('a_') && !empty($this->user->data['is_registered'])) ? append_sid("{$this->admin_path}index.{$this->php_ext}", false, true, $this->user->session_id) : '',
+				'U_ACP'					=> ($this->auth->acl_get('a_') && !empty($this->user->data['is_registered'])) ? append_sid("{$this->admin_path}index.{$this->php_ext}") : '',
 		]);
 
 		if ($run_cron)
diff --git a/phpBB/phpbb/log/log.php b/phpBB/phpbb/log/log.php
index 6142246477..988fa6f705 100644
--- a/phpBB/phpbb/log/log.php
+++ b/phpBB/phpbb/log/log.php
@@ -748,7 +748,7 @@ class log implements \phpbb\log\log_interface
 			{
 				$log[$key]['viewtopic'] = (isset($topic_auth['f_read'][$row['topic_id']])) ? append_sid("{$this->phpbb_root_path}viewtopic.{$this->php_ext}", 'f=' . $topic_auth['f_read'][$row['topic_id']] . '&amp;t=' . $row['topic_id']) : false;
 				$log[$key]['viewpost'] = (isset($topic_auth['f_read'][$row['topic_id']]) && $row['post_id']) ? append_sid("{$this->phpbb_root_path}viewtopic.{$this->php_ext}", 'f=' . $topic_auth['f_read'][$row['topic_id']] . '&amp;t=' . $row['topic_id'] . '&amp;p=' . $row['post_id'] . '#p' . $row['post_id']) : false;
-				$log[$key]['viewlogs'] = (isset($topic_auth['m_'][$row['topic_id']])) ? append_sid("{$this->phpbb_root_path}mcp.{$this->php_ext}", 'i=logs&amp;mode=topic_logs&amp;t=' . $row['topic_id'], true, $this->user->session_id) : false;
+				$log[$key]['viewlogs'] = (isset($topic_auth['m_'][$row['topic_id']])) ? append_sid("{$this->phpbb_root_path}mcp.{$this->php_ext}", 'i=logs&amp;mode=topic_logs&amp;t=' . $row['topic_id']) : false;
 			}
 		}
 
diff --git a/phpBB/phpbb/session.php b/phpBB/phpbb/session.php
index 4c911da894..fb93539b7d 100644
--- a/phpBB/phpbb/session.php
+++ b/phpBB/phpbb/session.php
@@ -272,8 +272,8 @@ class session
 			$this->cookie_data['k'] = $request->variable($config['cookie_name'] . '_k', '', false, \phpbb\request\request_interface::COOKIE);
 			$this->session_id 		= $request->variable($config['cookie_name'] . '_sid', '', false, \phpbb\request\request_interface::COOKIE);
 
-			$SID = (defined('NEED_SID')) ? '?sid=' . $this->session_id : '?sid=';
-			$_SID = (defined('NEED_SID')) ? $this->session_id : '';
+			$SID = '?sid=';
+			$_SID = '';
 
 			if (empty($this->session_id))
 			{
@@ -343,14 +343,6 @@ class session
 			}
 		}
 
-		// if no session id is set, redirect to index.php
-		$session_id = $request->variable('sid', '');
-		if (defined('NEED_SID') && (empty($session_id) || $this->session_id !== $session_id))
-		{
-			send_status_line(401, 'Unauthorized');
-			redirect(append_sid("{$phpbb_root_path}index.$phpEx"));
-		}
-
 		// if session id is set
 		if (!empty($this->session_id))
 		{
diff --git a/phpBB/viewtopic.php b/phpBB/viewtopic.php
index fe5190f4b6..3bb07da9df 100644
--- a/phpBB/viewtopic.php
+++ b/phpBB/viewtopic.php
@@ -645,9 +645,7 @@ $s_quickmod_action = append_sid(
 		'start'		=> $start,
 		'quickmod'	=> 1,
 		'redirect'	=> urlencode(str_replace('&amp;', '&', $viewtopic_url)),
-	),
-	true,
-	$user->session_id
+	)
 );
 
 $quickmod_array = array(