Index: src/wp-includes/kses.php
===================================================================
--- src/wp-includes/kses.php	(revision 33902)
+++ src/wp-includes/kses.php	(working copy)
@@ -1099,6 +1099,10 @@
 	. '(?:'               // Attribute value.
 	.     '\s*=\s*'       // All values begin with '='
 	.     '(?:'
+	.         '"(?:[^"[]*\[[^\]]*\])+[^"]*"'   // Double-quoted with embedded shortcode.
+	.     '|'
+	.         "'(?:[^'[]*\[[^\]]*\])+[^']*'"   // Single-quoted with embedded shortcode.
+	.     '|'
 	.         '"[^"]*"'   // Double-quoted
 	.     '|'
 	.         "'[^']*'"   // Single-quoted