diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 7a58329c82..2e8d7a3010 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -870,6 +870,8 @@ function img_caption_shortcode( $attr, $content = null ) {
 			$content = $matches[1];
 			$attr['caption'] = trim( $matches[2] );
 		}
+	} elseif ( strpos( $attr['caption'], '<' ) !== false ) {
+		$attr['caption'] = wp_kses( $attr['caption'], 'post' );
 	}
 
 	/**
diff --git a/src/wp-includes/shortcodes.php b/src/wp-includes/shortcodes.php
index 45df890e3e..e28e2b52f7 100644
--- a/src/wp-includes/shortcodes.php
+++ b/src/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);
 	}