Ticket #26649: 26649-fixed.patch

src/wp-includes/shortcodes.php

@@ -193 +193 @@
         // allow [[foo]] syntax for escaping a tag
-        if ( $m[1] == '[' && $m[6] == ']' ) {
-                return substr( $m[0], 1, -1 );
-        }
-        return $m[1] . $m[6];
+        if ( $m[1] == '[' && $m[6] == ']' ) {
+                // Return HTML entity for the left square bracket to prevent unwanted shortcode expansion.
+                return '[' . substr( $m[0], 2, -1 );
+        }
+
+        // Default behavior: return first and last matched characters.
+        return $m[1] . $m[6];
 }
 
 /**
  * Search content for shortcodes and filter shortcodes through their hooks.
  *
  * If there are no shortcode tags defined, then the content will be returned
  * without any filtering. This might cause issues when using the 'get_the_excerpt'
  * filter, so ensure shortcodes are correctly escaped.