Update 'Secure string handling'

Add information about possible path traversal attack with example

doc/JSON-RPC-interface.md

@@ -89,12 +89,13 @@ RPC interface will be abused.
   escaping of data beyond what's necessary to encode it as JSON,
   although it does usually provide serialized data using a hex
   representation of the bytes. If you use RPC data in your programs or
-  provide its data to other programs, you must ensure any problem
-  strings are properly escaped.  For example, multiple websites have
-  been manipulated because they displayed decoded hex strings that
-  included HTML `<script>` tags.  For this reason, and other
-  non-security reasons, it is recommended to display all serialized data
-  in hex form only.
+  provide its data to other programs, you must ensure any problem strings
+  are properly escaped. For example, the `createwallet` RPC accepts
+  arguments such as `wallet_name` which is a string and could be used
+  for a path traversal attack without application level checks. Multiple
+  websites have been manipulated because they displayed decoded hex strings
+  that included HTML `<script>` tags. For this reason, and others, it is
+  recommended to display all serialized data in hex form only.
 
 ## RPC consistency guarantees