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String Functions, escape for XSS

This example demonstrates the string function escape for preventing XSS.

Other versions: 7.31 | 7.40 | 7.54

Source Code

    CONSTANTS xss_demo TYPE string
                       VALUE `foo" onmouseover="alert('Gotcha!')`.

    DATA: query TYPE string VALUE `ABAP Objects`,
          esc_flag  TYPE abap_bool VALUE abap_true,
          xss_flag  TYPE abap_bool VALUE abap_false.

      in->add_field( EXPORTING text = 'Input'
                     CHANGING field = query
       )->add_field( EXPORTING text = 'Escape'
                               as_checkbox = abap_true
                     CHANGING field =  esc_flag
       )->request(   EXPORTING text = 'XSS-Demo'
                               as_checkbox = abap_true
                     CHANGING field =  xss_flag ).
      IF query IS INITIAL AND xss_flag = abap_false.

      IF xss_flag = abap_true.
        query = escape( val    = xss_demo
                        format = cl_abap_format=>e_xss_ml ).
        xss_flag = abap_false.

      IF esc_flag = abap_true.
        query = escape( val    = query
                        format = cl_abap_format=>e_xss_ml ).
      ELSEIF query <> xss_demo.
          `Without escaping only the prepared XSS-Demo is allowed.`
          TYPE 'I'.

      DATA(html) =
        `<html>`  &&
        `<body>`  &&
        `<p><a href="` && icf_node &&
        `?query=` && query &&
        `">Search in ABAP Documentation</a></p>` &&
        `<p><a href="` &&
        query && `">Search with Google</a></p>` &&
        `</body>` &&
        `</html>` ##no_text.
      cl_abap_browser=>show_html( html_string  = html
                                 buttons      = abap_true
                                 check_html   = abap_false
                                 context_menu = abap_true ).


A search term can be entered in a dialog box. An output window provides a search function in the ABAP keyword documentation and with an external search engine. By default, the input is escaped using the function escape and the format cl_abap_format=>e_xss_ml. This prevents cross site scripting (XSS).

The function can be disabled for specific input, which demonstrates the effects of an XSS attack. The input makes the links on the output window and the following input field unusable. More harmful functions could be used instead of the JavaScript function alert, but are not permitted in this example.