diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index d9c64f5bfe..0d020c11b4 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -4241,10 +4241,10 @@ function get_page_by_path( $page_path, $output = OBJECT, $post_type = 'page' ) {
 	$page_path = str_replace('%2F', '/', $page_path);
 	$page_path = str_replace('%20', ' ', $page_path);
 	$parts = explode( '/', trim( $page_path, '/' ) );
-	$parts = esc_sql( $parts );
 	$parts = array_map( 'sanitize_title_for_query', $parts );
+	$escaped_parts = esc_sql( $parts );
 
-	$in_string = "'" . implode( "','", $parts ) . "'";
+	$in_string = "'" . implode( "','", $escaped_parts ) . "'";
 
 	if ( is_array( $post_type ) ) {
 		$post_types = $post_type;
diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index 0b5a55e81f..553cd39d9f 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -1168,20 +1168,22 @@ class wpdb {
 	function _real_escape( $string ) {
 		if ( $this->dbh ) {
 			if ( $this->use_mysqli ) {
-				return mysqli_real_escape_string( $this->dbh, $string );
+				$escaped = mysqli_real_escape_string( $this->dbh, $string );
 			} else {
-				return mysql_real_escape_string( $string, $this->dbh );
+				$escaped = mysql_real_escape_string( $string, $this->dbh );
 			}
+		} else {
+			$class = get_class( $this );
+			if ( function_exists( '__' ) ) {
+				/* translators: %s: database access abstraction class, usually wpdb or a class extending wpdb */
+				_doing_it_wrong( $class, sprintf( __( '%s must set a database connection for use with escaping.' ), $class ), '3.6.0' );
+			} else {
+				_doing_it_wrong( $class, sprintf( '%s must set a database connection for use with escaping.', $class ), '3.6.0' );
+			}
+			$escaped = addslashes( $string );
 		}
 
-		$class = get_class( $this );
-		if ( function_exists( '__' ) ) {
-			/* translators: %s: database access abstraction class, usually wpdb or a class extending wpdb */
-			_doing_it_wrong( $class, sprintf( __( '%s must set a database connection for use with escaping.' ), $class ), '3.6.0' );
-		} else {
-			_doing_it_wrong( $class, sprintf( '%s must set a database connection for use with escaping.', $class ), '3.6.0' );
-		}
-		return addslashes( $string );
+		return $this->add_placeholder_escape( $escaped );
 	}
 
 	/**
@@ -1257,67 +1259,120 @@ class wpdb {
 	/**
 	 * Prepares a SQL query for safe execution. Uses sprintf()-like syntax.
 	 *
-	 * The following directives can be used in the query format string:
+	 * The following placeholders can be used in the query string:
 	 *   %d (integer)
 	 *   %f (float)
 	 *   %s (string)
-	 *   %% (literal percentage sign - no argument needed)
 	 *
-	 * All of %d, %f, and %s are to be left unquoted in the query string and they need an argument passed for them.
-	 * Literals (%) as parts of the query must be properly written as %%.
+	 * All placeholders MUST be left unquoted in the query string. A corresponding argument MUST be passed for each placeholder.
 	 *
-	 * This function only supports a small subset of the sprintf syntax; it only supports %d (integer), %f (float), and %s (string).
-	 * Does not support sign, padding, alignment, width or precision specifiers.
-	 * Does not support argument numbering/swapping.
+	 * For compatibility with old behavior, numbered or formatted string placeholders (eg, %1$s, %5s) will not have quotes
+	 * added by this function, so should be passed with appropriate quotes around them for your usage.
 	 *
-	 * May be called like {@link https://secure.php.net/sprintf sprintf()} or like {@link https://secure.php.net/vsprintf vsprintf()}.
+	 * Literal percentage signs (%) in the query string must be written as %%. Percentage wildcards (for example,
+	 * to use in LIKE syntax) must be passed via a substitution argument containing the complete LIKE string, these
+	 * cannot be inserted directly in the query string. Also see {@see esc_like()}.
 	 *
-	 * Both %d and %s should be left unquoted in the query string.
+	 * Arguments may be passed as individual arguments to the method, or as a single array containing all arguments. A combination
+	 * of the two is not supported.
 	 *
-	 *     $wpdb->prepare( "SELECT * FROM `table` WHERE `column` = %s AND `field` = %d", 'foo', 1337 );
+	 * Examples:
+	 *     $wpdb->prepare( "SELECT * FROM `table` WHERE `column` = %s AND `field` = %d OR `other_field` LIKE %s", array( 'foo', 1337, '%bar' ) );
 	 *     $wpdb->prepare( "SELECT DATE_FORMAT(`field`, '%%c') FROM `table` WHERE `column` = %s", 'foo' );
 	 *
 	 * @link https://secure.php.net/sprintf Description of syntax.
 	 * @since 2.3.0
 	 *
 	 * @param string      $query    Query statement with sprintf()-like placeholders
-	 * @param array|mixed $args     The array of variables to substitute into the query's placeholders if being called like
-	 *                              {@link https://secure.php.net/vsprintf vsprintf()}, or the first variable to substitute into the query's placeholders if
-	 *                              being called like {@link https://secure.php.net/sprintf sprintf()}.
-	 * @param mixed       $args,... further variables to substitute into the query's placeholders if being called like
-	 *                              {@link https://secure.php.net/sprintf sprintf()}.
+	 * @param array|mixed $args     The array of variables to substitute into the query's placeholders if being called with an array of arguments,
+	 *                              or the first variable to substitute into the query's placeholders if being called with individual arguments.
+	 * @param mixed       $args,... further variables to substitute into the query's placeholders if being called wih individual arguments.
 	 * @return string|void Sanitized query string, if there is a query to prepare.
 	 */
 	public function prepare( $query, $args ) {
-		if ( is_null( $query ) )
+		if ( is_null( $query ) ) {
 			return;
+		}
 
 		// This is not meant to be foolproof -- but it will catch obviously incorrect usage.
 		if ( strpos( $query, '%' ) === false ) {
+			wp_load_translations_early();
 			_doing_it_wrong( 'wpdb::prepare', sprintf( __( 'The query argument of %s must have a placeholder.' ), 'wpdb::prepare()' ), '3.9.0' );
 		}
 
 		$args = func_get_args();
 		array_shift( $args );
 
-		// If args were passed as an array (as in vsprintf), move them up
+		// If args were passed as an array (as in vsprintf), move them up.
+		$passed_as_array = false;
 		if ( is_array( $args[0] ) && count( $args ) == 1 ) {
+			$passed_as_array = true;
 			$args = $args[0];
 		}
 
 		foreach ( $args as $arg ) {
 			if ( ! is_scalar( $arg ) && ! is_null( $arg ) ) {
-				_doing_it_wrong( 'wpdb::prepare', sprintf( 'Unsupported value type (%s).', gettype( $arg ) ), '4.7.6' );
+				wp_load_translations_early();
+				_doing_it_wrong( 'wpdb::prepare', sprintf( __( 'Unsupported value type (%s).' ), gettype( $arg ) ), '4.8.2' );
+			}
+		}
+
+		/*
+		 * Specify the formatting allowed in a placeholder. The following are allowed:
+		 *
+		 * - Sign specifier. eg, $+d
+		 * - Numbered placeholders. eg, %1$s
+		 * - Padding specifier, including custom padding characters. eg, %05s, %'#5s
+		 * - Alignment specifier. eg, %05-s
+		 * - Precision specifier. eg, %.2f
+		 */
+		$allowed_format = '(?:[1-9][0-9]*[$])?[-+0-9]*(?: |0|\'.)?[-+0-9]*(?:\.[0-9]+)?';
+
+		/*
+		 * If a %s placeholder already has quotes around it, removing the existing quotes and re-inserting them
+		 * ensures the quotes are consistent.
+		 *
+		 * For backwards compatibility, this is only applied to %s, and not to placeholders like %1$s, which are frequently
+		 * used in the middle of longer strings, or as table name placeholders.
+		 */
+		$query = str_replace( "'%s'", '%s', $query ); // Strip any existing single quotes.
+		$query = str_replace( '"%s"', '%s', $query ); // Strip any existing double quotes.
+		$query = preg_replace( '/(?<!%)%s/', "'%s'", $query ); // Quote the strings, avoiding escaped strings like %%s.
+
+		$query = preg_replace( "/(?<!%)(%($allowed_format)?f)/" , '%\\2F', $query ); // Force floats to be locale unaware.
+
+		$query = preg_replace( "/%(?:%|$|(?!($allowed_format)?[sdF]))/", '%%\\1', $query ); // Escape any unescaped percents.
+
+		// Count the number of valid placeholders in the query.
+		$placeholders = preg_match_all( "/(^|[^%]|(%%)+)%($allowed_format)?[sdF]/", $query, $matches );
+
+		if ( count( $args ) !== $placeholders ) {
+			if ( 1 === $placeholders && $passed_as_array ) {
+				// If the passed query only expected one argument, but the wrong number of arguments were sent as an array, bail.
+				wp_load_translations_early();
+				_doing_it_wrong( 'wpdb::prepare', __( 'The query only expected one placeholder, but an array of multiple placeholders was sent.' ), '4.9.0' );
+
+				return;
+			} else {
+				/*
+				 * If we don't have the right number of placeholders, but they were passed as individual arguments,
+				 * or we were expecting multiple arguments in an array, throw a warning.
+				 */
+				wp_load_translations_early();
+				_doing_it_wrong( 'wpdb::prepare',
+					/* translators: 1: number of placeholders, 2: number of arguments passed */
+					sprintf( __( 'The query does not contain the correct number of placeholders (%1$d) for the number of arguments passed (%2$d).' ),
+						$placeholders,
+						count( $args ) ),
+					'4.8.3'
+				);
 			}
 		}
 
-		$query = str_replace( "'%s'", '%s', $query ); // in case someone mistakenly already singlequoted it
-		$query = str_replace( '"%s"', '%s', $query ); // doublequote unquoting
-		$query = preg_replace( '|(?<!%)%f|' , '%F', $query ); // Force floats to be locale unaware
-		$query = preg_replace( '|(?<!%)%s|', "'%s'", $query ); // quote the strings, avoiding escaped strings like %%s
-		$query = preg_replace( '/%(?:%|$|([^dsF]))/', '%%\\1', $query ); // escape any unescaped percents 
 		array_walk( $args, array( $this, 'escape_by_ref' ) );
-		return @vsprintf( $query, $args );
+		$query = @vsprintf( $query, $args );
+
+		return $this->add_placeholder_escape( $query );
 	}
 
 	/**
@@ -1895,6 +1950,64 @@ class wpdb {
 		}
 	}
 
+	/**
+	 * Generates and returns a placeholder escape string for use in queries returned by ::prepare().
+	 *
+	 * @since 4.8.3
+	 *
+	 * @return string String to escape placeholders.
+	 */
+	public function placeholder_escape() {
+		static $placeholder;
+
+		if ( ! $placeholder ) {
+			// If ext/hash is not present, compat.php's hash_hmac() does not support sha256.
+			$algo = function_exists( 'hash' ) ? 'sha256' : 'sha1';
+			// Old WP installs may not have AUTH_SALT defined.
+			$salt = defined( 'AUTH_SALT' ) ? AUTH_SALT : rand();
+
+			$placeholder = '{' . hash_hmac( $algo, uniqid( $salt, true ), $salt ) . '}';
+		}
+
+		/*
+		 * Add the filter to remove the placeholder escaper. Uses priority 0, so that anything
+		 * else attached to this filter will recieve the query with the placeholder string removed.
+		 */
+		if ( ! has_filter( 'query', array( $this, 'remove_placeholder_escape' ) ) ) {
+			add_filter( 'query', array( $this, 'remove_placeholder_escape' ), 0 );
+		}
+
+		return $placeholder;
+	}
+
+	/**
+	 * Adds a placeholder escape string, to escape anything that resembles a printf() placeholder.
+	 *
+	 * @since 4.8.3
+	 *
+	 * @param string $query The query to escape.
+	 * @return string The query with the placeholder escape string inserted where necessary.
+	 */
+	public function add_placeholder_escape( $query ) {
+		/*
+		 * To prevent returning anything that even vaguely resembles a placeholder,
+		 * we clobber every % we can find.
+		 */
+		return str_replace( '%', $this->placeholder_escape(), $query );
+	}
+
+	/**
+	 * Removes the placeholder escape strings from a query.
+	 *
+	 * @since 4.8.3
+	 *
+	 * @param string $query The query from which the placeholder will be removed.
+	 * @return string The query with the placeholder removed.
+	 */
+	public function remove_placeholder_escape( $query ) {
+		return str_replace( $this->placeholder_escape(), '%', $query );
+	}
+
 	/**
 	 * Insert a row into a table.
 	 *
diff --git a/tests/phpunit/tests/comment/query.php b/tests/phpunit/tests/comment/query.php
index ff4e3aced3..97aa4151cb 100644
--- a/tests/phpunit/tests/comment/query.php
+++ b/tests/phpunit/tests/comment/query.php
@@ -1218,22 +1218,24 @@ class Tests_Comment_Query extends WP_UnitTestCase {
 	 * @ticket 35513
 	 */
 	public function test_search_int_0_should_not_be_ignored() {
+		global $wpdb;
 		$q = new WP_Comment_Query();
 		$q->query( array(
 			'search' => 0,
 		) );
-		$this->assertContains( "comment_author LIKE '%0%'", $q->request );
+		$this->assertContains( "comment_author LIKE '%0%'", $wpdb->remove_placeholder_escape( $q->request ) );
 	}
 
 	/**
 	 * @ticket 35513
 	 */
 	public function test_search_string_0_should_not_be_ignored() {
+		global $wpdb;
 		$q = new WP_Comment_Query();
 		$q->query( array(
 			'search' => '0',
 		) );
-		$this->assertContains( "comment_author LIKE '%0%'", $q->request );
+		$this->assertContains( "comment_author LIKE '%0%'", $wpdb->remove_placeholder_escape( $q->request ) );
 	}
 
 	public function test_orderby_default() {
diff --git a/tests/phpunit/tests/date/query.php b/tests/phpunit/tests/date/query.php
index cc848be868..b5cfac8217 100644
--- a/tests/phpunit/tests/date/query.php
+++ b/tests/phpunit/tests/date/query.php
@@ -512,11 +512,12 @@ class Tests_WP_Date_Query extends WP_UnitTestCase {
 	 * @ticket 34228
 	 */
 	public function test_build_time_query_should_not_discard_hour_0() {
+		global $wpdb;
 		$q = new WP_Date_Query( array() );
 
 		$found = $q->build_time_query( 'post_date', '=', 0, 10 );
 
-		$this->assertContains( '%H', $found );
+		$this->assertContains( '%H', $wpdb->remove_placeholder_escape( $found ) );
 	}
 
 	public function test_build_time_query_compare_in() {
@@ -612,33 +613,36 @@ class Tests_WP_Date_Query extends WP_UnitTestCase {
 	}
 
 	public function test_build_time_query_hour_minute() {
+		global $wpdb;
 		$q = new WP_Date_Query( array() );
 
 		$found = $q->build_time_query( 'post_date', '=', 5, 15 );
 
 		// $compare value is floating point - use regex to account for
 		// varying precision on different PHP installations
-		$this->assertRegExp( "/DATE_FORMAT\( post_date, '%H\.%i' \) = 5\.150*/", $found );
+		$this->assertRegExp( "/DATE_FORMAT\( post_date, '%H\.%i' \) = 5\.150*/", $wpdb->remove_placeholder_escape( $found ) );
 	}
 
 	public function test_build_time_query_hour_minute_second() {
+		global $wpdb;
 		$q = new WP_Date_Query( array() );
 
 		$found = $q->build_time_query( 'post_date', '=', 5, 15, 35 );
 
 		// $compare value is floating point - use regex to account for
 		// varying precision on different PHP installations
-		$this->assertRegExp( "/DATE_FORMAT\( post_date, '%H\.%i%s' \) = 5\.15350*/", $found );
+		$this->assertRegExp( "/DATE_FORMAT\( post_date, '%H\.%i%s' \) = 5\.15350*/", $wpdb->remove_placeholder_escape( $found ) );
 	}
 
 	public function test_build_time_query_minute_second() {
+		global $wpdb;
 		$q = new WP_Date_Query( array() );
 
 		$found = $q->build_time_query( 'post_date', '=', null, 15, 35 );
 
 		// $compare value is floating point - use regex to account for
 		// varying precision on different PHP installations
-		$this->assertRegExp( "/DATE_FORMAT\( post_date, '0\.%i%s' \) = 0\.15350*/", $found );
+		$this->assertRegExp( "/DATE_FORMAT\( post_date, '0\.%i%s' \) = 0\.15350*/", $wpdb->remove_placeholder_escape( $found ) );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/db.php b/tests/phpunit/tests/db.php
index 26c324e81a..978cb6f274 100644
--- a/tests/phpunit/tests/db.php
+++ b/tests/phpunit/tests/db.php
@@ -270,6 +270,9 @@ class Tests_DB extends WP_UnitTestCase {
 	public function test_double_escaped_placeholders() {
 		global $wpdb;
 		$sql = $wpdb->prepare( "UPDATE test_table SET string_column = '%%f is a float, %%d is an int %d, %%s is a string', field = %s", 3, '4' );
+		$this->assertContains( $wpdb->placeholder_escape(), $sql );
+
+		$sql = $wpdb->remove_placeholder_escape( $sql );
 		$this->assertEquals( "UPDATE test_table SET string_column = '%f is a float, %d is an int 3, %s is a string', field = '4'", $sql );
 	}
 
@@ -375,8 +378,8 @@ class Tests_DB extends WP_UnitTestCase {
 		$this->assertEquals( "SELECT * FROM $wpdb->users WHERE id = 0 AND user_login = 'admin'", $prepared );
 	}
 
-        function test_prepare_vsprintf() {
-                global $wpdb;
+    function test_prepare_vsprintf() {
+		global $wpdb;
 
 		$prepared = $wpdb->prepare( "SELECT * FROM $wpdb->users WHERE id = %d AND user_login = %s", array( 1, "admin" ) );
 		$this->assertEquals( "SELECT * FROM $wpdb->users WHERE id = 1 AND user_login = 'admin'", $prepared );
@@ -393,7 +396,74 @@ class Tests_DB extends WP_UnitTestCase {
 
 		$prepared = @$wpdb->prepare( "SELECT * FROM $wpdb->users WHERE id = %d AND user_login = %s", array( array( 1 ), "admin" ) );
 		$this->assertEquals( "SELECT * FROM $wpdb->users WHERE id = 0 AND user_login = 'admin'", $prepared );
-        }
+	}
+
+	/**
+	 * @ticket 42040
+	 * @dataProvider data_prepare_incorrect_arg_count
+	 * @expectedIncorrectUsage wpdb::prepare
+	 */
+	public function test_prepare_incorrect_arg_count( $query, $args, $expected ) {
+		global $wpdb;
+
+		// $query is the first argument to be passed to wpdb::prepare()
+		array_unshift( $args, $query );
+
+		$prepared = @call_user_func_array( array( $wpdb, 'prepare' ), $args );
+		$this->assertEquals( $expected, $prepared );
+	}
+
+	public function data_prepare_incorrect_arg_count() {
+		global $wpdb;
+
+		return array(
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d AND user_login = %s",     // Query
+				array( 1, "admin", "extra-arg" ),                                   // ::prepare() args, to be passed via call_user_func_array
+				"SELECT * FROM $wpdb->users WHERE id = 1 AND user_login = 'admin'", // Expected output
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %%%d AND user_login = %s",
+				array( 1 ),
+				false,
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d AND user_login = %s",
+				array( array( 1, "admin", "extra-arg" ) ),
+				"SELECT * FROM $wpdb->users WHERE id = 1 AND user_login = 'admin'",
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d AND %% AND user_login = %s",
+				array( 1, "admin", "extra-arg" ),
+				"SELECT * FROM $wpdb->users WHERE id = 1 AND {$wpdb->placeholder_escape()} AND user_login = 'admin'",
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %%%d AND %F AND %f AND user_login = %s",
+				array( 1, 2.3, "4.5", "admin", "extra-arg" ),
+				"SELECT * FROM $wpdb->users WHERE id = {$wpdb->placeholder_escape()}1 AND 2.300000 AND 4.500000 AND user_login = 'admin'",
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d AND user_login = %s",
+				array( array( 1 ), "admin", "extra-arg" ),
+				"SELECT * FROM $wpdb->users WHERE id = 0 AND user_login = 'admin'",
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d and user_nicename = %s and user_status = %d and user_login = %s",
+				array( 1, "admin", 0 ),
+				'',
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d and user_nicename = %s and user_status = %d and user_login = %s",
+				array( array( 1, "admin", 0 ) ),
+				'',
+			),
+			array(
+				"SELECT * FROM $wpdb->users WHERE id = %d and %% and user_login = %s and user_status = %d and user_login = %s",
+				array( 1, "admin", "extra-arg" ),
+				'',
+			),
+		);
+	}
 
 	function test_db_version() {
 		global $wpdb;
@@ -1118,12 +1188,326 @@ class Tests_DB extends WP_UnitTestCase {
 	}
 
 	/**
-	 *
+	 * @dataProvider data_prepare_with_placeholders
 	 */
-	function test_prepare_with_unescaped_percents() {
+	function test_prepare_with_placeholders_and_individual_args( $sql, $values, $incorrect_usage, $expected) {
 		global $wpdb;
 
-		$sql = $wpdb->prepare( '%d %1$d %%% %', 1 );
-		$this->assertEquals( '1 %1$d %% %', $sql );
+		if ( $incorrect_usage ) {
+			$this->setExpectedIncorrectUsage( 'wpdb::prepare' );
+		}
+
+		if ( ! is_array( $values ) ) {
+			$values = array( $values );
+		}
+
+		array_unshift( $values, $sql );
+
+		$sql = call_user_func_array( array( $wpdb, 'prepare' ), $values );
+		$this->assertEquals( $expected, $sql );
+	}
+
+	/**
+	 * @dataProvider data_prepare_with_placeholders
+	 */
+	function test_prepare_with_placeholders_and_array_args( $sql, $values, $incorrect_usage, $expected) {
+		global $wpdb;
+
+		if ( $incorrect_usage ) {
+			$this->setExpectedIncorrectUsage( 'wpdb::prepare' );
+		}
+
+		if ( ! is_array( $values ) ) {
+			$values = array( $values );
+		}
+
+		$sql = call_user_func_array( array( $wpdb, 'prepare' ), array( $sql, $values ) );
+		$this->assertEquals( $expected, $sql );
+	}
+
+	function data_prepare_with_placeholders() {
+		global $wpdb;
+
+		return array(
+			array(
+				'%5s',   // SQL to prepare
+				'foo',   // Value to insert in the SQL
+				false,   // Whether to expect an incorrect usage error or not
+				'  foo', // Expected output
+			),
+			array(
+				'%1$d %%% % %%1$d%% %%%1$d%%',
+				1,
+				true,
+				"1 {$wpdb->placeholder_escape()}{$wpdb->placeholder_escape()} {$wpdb->placeholder_escape()} {$wpdb->placeholder_escape()}1\$d{$wpdb->placeholder_escape()} {$wpdb->placeholder_escape()}1{$wpdb->placeholder_escape()}",
+			),
+			array(
+				'%-5s',
+				'foo',
+				false,
+				'foo  ',
+			),
+			array(
+				'%05s',
+				'foo',
+				false,
+				'00foo',
+			),
+			array(
+				"%'#5s",
+				'foo',
+				false,
+				'##foo',
+			),
+			array(
+				'%.3s',
+				'foobar',
+				false,
+				'foo',
+			),
+			array(
+				'%.3f',
+				5.123456,
+				false,
+				'5.123',
+			),
+			array(
+				'%.3f',
+				5.12,
+				false,
+				'5.120',
+			),
+			array(
+				'%s',
+				' %s ',
+				false,
+				"' {$wpdb->placeholder_escape()}s '",
+			),
+			array(
+				'%1$s',
+				' %s ',
+				false,
+				" {$wpdb->placeholder_escape()}s ",
+			),
+			array(
+				'%1$s',
+				' %1$s ',
+				false,
+				" {$wpdb->placeholder_escape()}1\$s ",
+			),
+			array(
+				'%d %1$d %%% %',
+				1,
+				true,
+				"1 1 {$wpdb->placeholder_escape()}{$wpdb->placeholder_escape()} {$wpdb->placeholder_escape()}",
+			),
+			array(
+				'%d %2$s',
+				array( 1, 'hello' ),
+				false,
+				"1 hello",
+			),
+			array(
+				"'%s'",
+				'hello',
+				false,
+				"'hello'",
+			),
+			array(
+				'"%s"',
+				'hello',
+				false,
+				"'hello'",
+			),
+			array(
+				"%s '%1\$s'",
+				'hello',
+				true,
+				"'hello' 'hello'",
+			),
+			array(
+				"%s '%1\$s'",
+				'hello',
+				true,
+				"'hello' 'hello'",
+			),
+			array(
+				'%s "%1$s"',
+				'hello',
+				true,
+				"'hello' \"hello\"",
+			),
+			array(
+				"%%s %%'%1\$s'",
+				'hello',
+				false,
+				"{$wpdb->placeholder_escape()}s {$wpdb->placeholder_escape()}'hello'",
+			),
+			array(
+				'%%s %%"%1$s"',
+				'hello',
+				false,
+				"{$wpdb->placeholder_escape()}s {$wpdb->placeholder_escape()}\"hello\"",
+			),
+			array(
+				'%s',
+				' %  s ',
+				false,
+				"' {$wpdb->placeholder_escape()}  s '",
+			),
+			array(
+				'%%f %%"%1$f"',
+				3,
+				false,
+				"{$wpdb->placeholder_escape()}f {$wpdb->placeholder_escape()}\"3.000000\"",
+			),
+			array(
+				'WHERE second=\'%2$s\' AND first=\'%1$s\'',
+				array( 'first arg', 'second arg' ),
+				false,
+				"WHERE second='second arg' AND first='first arg'",
+			),
+			array(
+				'WHERE second=%2$d AND first=%1$d',
+				array( 1, 2 ),
+				false,
+				"WHERE second=2 AND first=1",
+			),
+			array(
+				"'%'%%s",
+				'hello',
+				true,
+				"'{$wpdb->placeholder_escape()}'{$wpdb->placeholder_escape()}s",
+			),
+			array(
+				"'%'%%s%s",
+				'hello',
+				false,
+				"'{$wpdb->placeholder_escape()}'{$wpdb->placeholder_escape()}s'hello'",
+			),
+			array(
+				"'%'%%s %s",
+				'hello',
+				false,
+				"'{$wpdb->placeholder_escape()}'{$wpdb->placeholder_escape()}s 'hello'",
+			),
+			array(
+				"'%-'#5s' '%'#-+-5s'",
+				array( 'hello', 'foo' ),
+				false,
+				"'hello' 'foo##'",
+			),
+		);
+	}
+
+	/**
+	 * @dataProvider data_escape_and_prepare
+	 */
+	function test_escape_and_prepare( $escape, $sql, $values, $incorrect_usage, $expected ) {
+		global $wpdb;
+
+		if ( $incorrect_usage ) {
+			$this->setExpectedIncorrectUsage( 'wpdb::prepare' );
+		}
+
+		$escape = esc_sql( $escape );
+
+		$sql = str_replace( '{ESCAPE}', $escape, $sql );
+
+		$actual = $wpdb->prepare( $sql, $values );
+
+		$this->assertEquals( $expected, $actual );
+	}
+
+	function data_escape_and_prepare() {
+		global $wpdb;
+		return array(
+			array(
+				'%s',                                  // String to pass through esc_url()
+				' {ESCAPE} ',                          // Query to insert the output of esc_url() into, replacing "{ESCAPE}"
+				'foo',                                 // Data to send to prepare()
+				true,                                  // Whether to expect an incorrect usage error or not
+				" {$wpdb->placeholder_escape()}s ",    // Expected output
+			),
+			array(
+				'foo%sbar',
+				"SELECT * FROM bar WHERE foo='{ESCAPE}' OR baz=%s",
+				array( ' SQLi -- -', 'pewpewpew' ),
+				true,
+				null,
+			),
+			array(
+				'%s',
+				' %s {ESCAPE} ',
+				'foo',
+				false,
+				" 'foo' {$wpdb->placeholder_escape()}s ",
+			),
+		);
+	}
+
+	/**
+	 * @expectedIncorrectUsage wpdb::prepare
+	 */
+	function test_double_prepare() {
+		global $wpdb;
+
+		$part = $wpdb->prepare( ' AND meta_value = %s', ' %s ' );
+		$this->assertNotContains( '%s', $part );
+		$query = $wpdb->prepare( 'SELECT * FROM {$wpdb->postmeta} WHERE meta_key = %s $part', array( 'foo', 'bar' ) );
+		$this->assertNull( $query );
+	}
+
+	function test_prepare_numeric_placeholders_float_args() {
+		global $wpdb;
+
+		$actual = $wpdb->prepare(
+			'WHERE second=%2$f AND first=%1$f',
+			1.1,
+			2.2
+		);
+
+		/* Floats can be right padded, need to assert differently */
+		$this->assertContains( ' first=1.1', $actual );
+		$this->assertContains( ' second=2.2', $actual );
+	}
+
+	function test_prepare_numeric_placeholders_float_array() {
+		global $wpdb;
+
+		$actual = $wpdb->prepare(
+			'WHERE second=%2$f AND first=%1$f',
+			array( 1.1, 2.2 )
+		);
+
+		/* Floats can be right padded, need to assert differently */
+		$this->assertContains( ' first=1.1', $actual );
+		$this->assertContains( ' second=2.2', $actual );
+	}
+
+	function test_query_unescapes_placeholders() {
+		global $wpdb;
+
+		$value = ' %s ';
+
+		$wpdb->query( "CREATE TABLE {$wpdb->prefix}test_placeholder( a VARCHAR(100) );" );
+		$sql = $wpdb->prepare( "INSERT INTO {$wpdb->prefix}test_placeholder VALUES(%s)", $value );
+		$wpdb->query( $sql );
+
+		$actual = $wpdb->get_var( "SELECT a FROM {$wpdb->prefix}test_placeholder" );
+
+		$wpdb->query( "DROP TABLE {$wpdb->prefix}test_placeholder" );
+
+		$this->assertNotContains( '%s', $sql );
+		$this->assertEquals( $value, $actual );
+	}
+
+	function test_esc_sql_with_unsupported_placeholder_type() {
+		global $wpdb;
+
+		$sql = $wpdb->prepare( ' %s %1$c ', 'foo' );
+		$sql = $wpdb->prepare( " $sql %s ", 'foo' );
+
+		$this->assertEquals( "  'foo' {$wpdb->placeholder_escape()}1\$c  'foo' ", $sql );
 	}
 }
diff --git a/tests/phpunit/tests/rest-api/rest-posts-controller.php b/tests/phpunit/tests/rest-api/rest-posts-controller.php
index db94b71d5f..49a51bb642 100644
--- a/tests/phpunit/tests/rest-api/rest-posts-controller.php
+++ b/tests/phpunit/tests/rest-api/rest-posts-controller.php
@@ -84,7 +84,7 @@ class WP_Test_REST_Posts_Controller extends WP_Test_REST_Post_Type_Controller_Te
 		global $wpdb;
 		$expected_clause = str_replace( '{posts}', $wpdb->posts, $pattern );
 		$this->assertCount( 1, $this->posts_clauses );
-		$this->assertEquals( $expected_clause, $this->posts_clauses[0][ $clause ] );
+		$this->assertEquals( $expected_clause, $wpdb->remove_placeholder_escape( $this->posts_clauses[0][ $clause ] ) );
 	}
 
 	public function assertPostsOrderedBy( $pattern ) {
diff --git a/tests/phpunit/tests/term/meta.php b/tests/phpunit/tests/term/meta.php
index ac309dc622..b88140aad4 100644
--- a/tests/phpunit/tests/term/meta.php
+++ b/tests/phpunit/tests/term/meta.php
@@ -358,7 +358,7 @@ class Tests_Term_Meta extends WP_UnitTestCase {
 
 		register_taxonomy( 'wptests_tax', 'post' );
 		$t1 = wp_insert_term( 'Foo', 'wptests_tax' );
-		add_term_meta( $t1, 'foo', 'bar' );
+		add_term_meta( $t1['term_id'], 'foo', 'bar' );
 
 		register_taxonomy( 'wptests_tax_2', 'post' );
 		register_taxonomy( 'wptests_tax_3', 'post' );
diff --git a/wp-tests-config-sample.php b/wp-tests-config-sample.php
index 3ea3c0296a..3965745805 100644
--- a/wp-tests-config-sample.php
+++ b/wp-tests-config-sample.php
@@ -38,6 +38,21 @@ define( 'DB_HOST', 'localhost' );
 define( 'DB_CHARSET', 'utf8' );
 define( 'DB_COLLATE', '' );
 
+/**#@+
+ * Authentication Unique Keys and Salts.
+ *
+ * Change these to different unique phrases!
+ * You can generate these using the {@link https://api.wordpress.org/secret-key/1.1/salt/ WordPress.org secret-key service}
+ */
+define('AUTH_KEY',         'put your unique phrase here');
+define('SECURE_AUTH_KEY',  'put your unique phrase here');
+define('LOGGED_IN_KEY',    'put your unique phrase here');
+define('NONCE_KEY',        'put your unique phrase here');
+define('AUTH_SALT',        'put your unique phrase here');
+define('SECURE_AUTH_SALT', 'put your unique phrase here');
+define('LOGGED_IN_SALT',   'put your unique phrase here');
+define('NONCE_SALT',       'put your unique phrase here');
+
 $table_prefix  = 'wptests_';   // Only numbers, letters, and underscores please!
 
 define( 'WP_TESTS_DOMAIN', 'example.org' );