Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

Description

This may allow such characters to be treated as control characters, which are executed client-side in the context of the user's session. Although this can be classified as an injection problem, the more pertinent issue is the improper conversion of such special characters to respective context-appropriate entities before displaying them to the user.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In the following example, a guestbook comment isn't properly encoded, filtered, or otherwise neutralized for script-related tags before being displayed in a client browser.

<% for (Iterator i = guestbook.iterator(); i.hasNext(); ) {
  Entry e = (Entry) i.next(); %>
  <p>Entry #<%= e.getId() %></p>
  <p><%= e.getText() %></p>
  <%
  } %>

See Also