diff --git a/src/wp-includes/class-wp-xmlrpc-server.php b/src/wp-includes/class-wp-xmlrpc-server.php
index 9d7a643bec..bf6c7b1cb5 100644
--- a/src/wp-includes/class-wp-xmlrpc-server.php
+++ b/src/wp-includes/class-wp-xmlrpc-server.php
@@ -45,6 +45,14 @@ class wp_xmlrpc_server extends IXR_Server {
 	 */
 	public $error;
 
+	/**
+	 * Flags that the user authentication has failed in this instance of wp_xmlrpc_server.
+	 *
+	 * @access protected
+	 * @var bool
+	 */
+	protected $auth_failed = false;
+
 	/**
 	 * Register all of the XMLRPC methods that XMLRPC server understands.
 	 *
@@ -251,11 +259,18 @@ class wp_xmlrpc_server extends IXR_Server {
 			return false;
 		}
 
-		$user = wp_authenticate($username, $password);
+		if ( $this->auth_failed ) {
+			$user = new WP_Error( 'login_prevented' );
+		} else {
+			$user = wp_authenticate( $username, $password );
+		}
 
-		if (is_wp_error($user)) {
+		if ( is_wp_error( $user ) ) {
 			$this->error = new IXR_Error( 403, __( 'Incorrect username or password.' ) );
 
+			// Flag that authentication has failed once on this wp_xmlrpc_server instance
+			$this->auth_failed = true;
+
 			/**
 			 * Filter the XML-RPC user login error message.
 			 *
diff --git a/tests/phpunit/includes/testcase-xmlrpc.php b/tests/phpunit/includes/testcase-xmlrpc.php
index 5fefb51422..9d268ce562 100644
--- a/tests/phpunit/includes/testcase-xmlrpc.php
+++ b/tests/phpunit/includes/testcase-xmlrpc.php
@@ -11,11 +11,14 @@ class WP_XMLRPC_UnitTestCase extends WP_UnitTestCase {
 
 		add_filter( 'pre_option_enable_xmlrpc', '__return_true' );
 
-		$this->myxmlrpcserver = new wp_xmlrpc_server();
+		$this->myxmlrpcserver = new WP_XMLRPC_Server_UnitTestable();
 	}
 
 	function tearDown() {
 		remove_filter( 'pre_option_enable_xmlrpc', '__return_true' );
+
+		 $this->myxmlrpcserver->reset_failed_auth();
+
 		$this->remove_added_uploads();
 
 		parent::tearDown();
@@ -29,3 +32,9 @@ class WP_XMLRPC_UnitTestCase extends WP_UnitTestCase {
 		));
 	}
 }
+
+class WP_XMLRPC_Server_UnitTestable extends wp_xmlrpc_server {
+	public function reset_failed_auth() {
+		$this->auth_failed = false;
+	}
+}
\ No newline at end of file
diff --git a/tests/phpunit/tests/xmlrpc/basic.php b/tests/phpunit/tests/xmlrpc/basic.php
index abfacc22c6..abe9e69eb6 100644
--- a/tests/phpunit/tests/xmlrpc/basic.php
+++ b/tests/phpunit/tests/xmlrpc/basic.php
@@ -19,10 +19,78 @@ class Tests_XMLRPC_Basic extends WP_XMLRPC_UnitTestCase {
 	function test_login_pass_ok() {
 		$user_id = $this->make_user_by_role( 'subscriber' );
 
-		$this->assertFalse( $this->myxmlrpcserver->login_pass_ok( 'username', 'password' ) );
-		$this->assertFalse( $this->myxmlrpcserver->login( 'username', 'password' ) );
-
 		$this->assertTrue( $this->myxmlrpcserver->login_pass_ok( 'subscriber', 'subscriber' ) );
 		$this->assertInstanceOf( 'WP_User', $this->myxmlrpcserver->login( 'subscriber', 'subscriber' ) );
 	}
+
+	function test_login_pass_bad() {
+		$user_id = $this->make_user_by_role( 'subscriber' );
+
+		$this->assertFalse( $this->myxmlrpcserver->login_pass_ok( 'username', 'password' ) );
+		$this->assertFalse( $this->myxmlrpcserver->login( 'username', 'password' ) );
+
+		// The auth will still fail due to authentication blocking after the first failed attempt
+		$this->assertFalse( $this->myxmlrpcserver->login_pass_ok( 'subscriber', 'subscriber' ) );
+	}
+
+	/**
+	 * @ticket 34336
+	 */
+	function test_multicall_invalidates_all_calls_after_invalid_call() {
+		$editor_id = $this->make_user_by_role( 'editor' );
+		$post_id = self::factory()->post->create( array(
+			'post_author' => $editor_id,
+		) );
+
+		$method_calls = array(
+			// Valid login
+			array(
+				'methodName' => 'wp.editPost',
+				'params'     => array(
+					0,
+					'editor',
+					'editor',
+					$post_id,
+					array(
+						'title' => 'Title 1',
+					),
+				),
+			),
+			// *Invalid* login
+			array(
+				'methodName' => 'wp.editPost',
+				'params'     => array(
+					0,
+					'editor',
+					'password',
+					$post_id,
+					array(
+						'title' => 'Title 2',
+					),
+				),
+			),
+			// Valid login
+			array(
+				'methodName' => 'wp.editPost',
+				'params'     => array(
+					0,
+					'editor',
+					'editor',
+					$post_id,
+					array(
+						'title' => 'Title 3',
+					),
+				),
+			),
+		);
+
+		$this->myxmlrpcserver->callbacks = $this->myxmlrpcserver->methods;
+
+		$result = $this->myxmlrpcserver->multiCall( $method_calls );
+
+		$this->assertArrayNotHasKey( 'faultCode', $result[0] );
+		$this->assertArrayHasKey( 'faultCode', $result[1] );
+		$this->assertArrayHasKey( 'faultCode', $result[2] );
+
+	}
 }
\ No newline at end of file