Index: tests/phpunit/tests/query/results.php
===================================================================
--- tests/phpunit/tests/query/results.php	(revision 25277)
+++ tests/phpunit/tests/query/results.php	(working copy)
@@ -486,4 +486,51 @@
 		$author_ids = array_unique( wp_list_pluck( $posts, 'post_author' ) );
 		$this->assertEqualSets( array( $author_1 ), $author_ids );
 	}
+
+	/**
+	 * @ticket 10935
+	 */
+	function test_query_is_date() {
+		$this->q->query( array(
+			'year' => '2007',
+			'monthnum' => '01',
+			'day' => '01',
+		) );
+
+		$this->assertTrue( $this->q->is_date );
+		$this->assertTrue( $this->q->is_day );
+		$this->assertFalse( $this->q->is_month );
+		$this->assertFalse( $this->q->is_year );
+
+		$this->q->query( array(
+			'year' => '2007',
+			'monthnum' => '01',
+		) );
+
+		$this->assertTrue( $this->q->is_date );
+		$this->assertFalse( $this->q->is_day );
+		$this->assertTrue( $this->q->is_month );
+		$this->assertFalse( $this->q->is_year );
+
+		$this->q->query( array(
+			'year' => '2007',
+		) );
+
+		$this->assertTrue( $this->q->is_date );
+		$this->assertFalse( $this->q->is_day );
+		$this->assertFalse( $this->q->is_month );
+		$this->assertTrue( $this->q->is_year );
+
+		$this->q->query( array(
+			'year' => '2007',
+			'monthnum' => '01',
+			'day' => '50',
+		) );
+
+		$this->assertTrue( $this->q->is_404 );
+		$this->assertFalse( $this->q->is_date );
+		$this->assertFalse( $this->q->is_day );
+		$this->assertFalse( $this->q->is_month );
+		$this->assertFalse( $this->q->is_year );
+	}
 }
Index: tests/phpunit/tests/query/conditionals.php
===================================================================
--- tests/phpunit/tests/query/conditionals.php	(revision 25277)
+++ tests/phpunit/tests/query/conditionals.php	(working copy)
@@ -629,4 +629,12 @@
 	// '[0-9]{4}/[0-9]{1,2}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/trackback/?$' => 'index.php?attachment=$matches[1]&tb=1',
 	// '[0-9]{4}/[0-9]{1,2}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$' => 'index.php?attachment=$matches[1]&feed=$matches[2]',
 	// '[0-9]{4}/[0-9]{1,2}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/(feed|rdf|rss|rss2|atom)/?$' => 'index.php?attachment=$matches[1]&feed=$matches[2]',
+
+	function test_bad_dates() {
+		$this->go_to( '/2013/13/13/' );
+		$this->assertQueryTrue( 'is_404' );
+
+		$this->go_to( '/2013/11/41/' );
+		$this->assertQueryTrue( 'is_404' );
+	}
 }
Index: tests/phpunit/tests/canonical.php
===================================================================
--- tests/phpunit/tests/canonical.php	(revision 25277)
+++ tests/phpunit/tests/canonical.php	(working copy)
@@ -239,6 +239,9 @@
 
 			array( '/?year=2008', '/2008/'),
 
+			array( '/2012/13/', '/2012/'),
+			array( '/2012/11/51/', '/2012/11/'),
+
 			// Authors
 			array( '/?author=%d', '/author/canonical-author/' ),
 //			array( '/?author=%d&year=2008', '/2008/?author=3'),
Index: src/wp-includes/query.php
===================================================================
--- src/wp-includes/query.php	(revision 25277)
+++ src/wp-includes/query.php	(working copy)
@@ -1513,15 +1513,24 @@
 
 			if ( $qv['day'] ) {
 				if ( ! $this->is_date ) {
-					$this->is_day = true;
-					$this->is_date = true;
+					$date = sprintf( '%04d-%02d-%02d', $qv['year'], $qv['monthnum'], $qv['day'] );
+					if ( $qv['monthnum'] && $qv['year'] && ! wp_checkdate( $qv['monthnum'], $qv['day'], $qv['year'], $date ) ) {
+						$qv['error'] = '404';
+					} else {
+						$this->is_day = true;
+						$this->is_date = true;
+					}
 				}
 			}
 
 			if ( $qv['monthnum'] ) {
 				if ( ! $this->is_date ) {
-					$this->is_month = true;
-					$this->is_date = true;
+					if ( 12 < $qv['monthnum'] ) {
+						$qv['error'] = '404';
+					} else {
+						$this->is_month = true;
+						$this->is_date = true;
+					}
 				}
 			}
 
Index: src/wp-includes/canonical.php
===================================================================
--- src/wp-includes/canonical.php	(revision 25277)
+++ src/wp-includes/canonical.php	(working copy)
@@ -101,6 +101,20 @@
 			}
 		}
 
+		if ( get_query_var( 'day' ) && get_query_var( 'monthnum' ) && get_query_var( 'year' ) ) {
+			$year  = get_query_var( 'year' );
+			$month = get_query_var( 'monthnum' );
+			$day   = get_query_var( 'day' );
+			$date  = sprintf( '%04d-%02d-%02d', $year, $month, $day );
+			if ( ! wp_checkdate( $month, $day, $year, $date ) ) {
+				$redirect_url = get_month_link( $year, $month );
+				$redirect['query'] = _remove_qs_args_if_not_in_url( $redirect['query'], array( 'year', 'monthnum', 'day' ), $redirect_url );
+			}
+		} elseif ( get_query_var( 'monthnum' ) && get_query_var( 'year' ) && 12 < get_query_var( 'monthnum' ) ) {
+			$redirect_url = get_year_link( get_query_var( 'year' ) );
+			$redirect['query'] = _remove_qs_args_if_not_in_url( $redirect['query'], array( 'year', 'monthnum' ), $redirect_url );
+		}
+
 		if ( ! $redirect_url ) {
 			if ( $redirect_url = redirect_guess_404_permalink() ) {
 				$redirect['query'] = _remove_qs_args_if_not_in_url( $redirect['query'], array( 'page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type' ), $redirect_url );