Uncaught Exception in Servlet

Description

When a Servlet throws an exception, the default error response the Servlet container sends back to the user typically includes debugging information. This information is of great value to an attacker. For example, a stack trace might show the attacker a malformed SQL query string, the type of database being used, and the version of the application container. This information enables the attacker to target known vulnerabilities in these components.

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

The following example attempts to resolve a hostname.

protected void doPost (HttpServletRequest req, HttpServletResponse res) throws IOException {
  String ip = req.getRemoteAddr();
  InetAddress addr = InetAddress.getByName(ip);
  ...
  out.println("hello " + addr.getHostName());
}

A DNS lookup failure will cause the Servlet to throw an exception.

See Also