Shortcodes: don't allow unclosed HTML elements in attributes

Built from https://develop.svn.wordpress.org/trunk@34134


git-svn-id: http://core.svn.wordpress.org/trunk@34102 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/shortcodes.php

@@ -462,6 +462,15 @@ function shortcode_parse_atts($text) {
 			elseif (isset($m[8]))
 				$atts[] = stripcslashes($m[8]);
 		}
+
+		// Reject any unclosed HTML elements
+		foreach( $atts as &$value ) {
+			if ( false !== strpos( $value, '<' ) ) {
+				if ( 1 !== preg_match( '/^[^<]*+(?:<[^>]*+>[^<]*+)*+$/', $value ) ) {
+					$value = '';
+				}
+			}
+		}
 	} else {
 		$atts = ltrim($text);
 	}