Difference between revisions of "CRV2 ContextEncJscriptParams"

Revision as of 13:21, 21 October 2013

Untrusted data, if being placed inside a Javascript function/code requires validation. Unvalidated data may break out of the data context and wind up being executed in the code context on a users browser.

Examples of exploitation points (sinks) which are worth reviewing for:

    <script>var currentValue='UNTRUSTED DATA';</script> 
    <script>someFunction('UNTRUSTED DATA');</script> 
    attack: ');/* BAD STUFF */
    

Potential solutions:

OWASP HTML sanatiser Project
OWASP JSON Sanitizer Project

ESAPI javascript escaping can be call in this manner:

    String safe = ESAPI.encoder().encodeForJavaScript( request.getParameter( "input" ) );

Please note there are some JavaScript functions that can never safely use untrusted data as input - EVEN IF JAVASCRIPT ESCAPED!

For example:

    <script>
    window.setInterval('...EVEN IF YOU ESCAPE UNTRUSTED DATA YOU ARE XSSED HERE...');
    </script>

    var txtField = "A1";
    var txtUserInput = "'[email protected]';alert(1);";
    eval(   "document.forms[0]." + txtField + ".value =" + A1);