Java Runtime Error Message Containing Sensitive Information

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 Java example the class InputFileRead enables an input file to be read using a FileReader object. In the constructor of this class a default input file path is set to some directory on the local file system and the method setInputFile must be called to set the name of the input file to be read in the default directory. The method readInputFile will create the FileReader object and will read the contents of the file. If the method setInputFile is not called prior to calling the method readInputFile then the File object will remain null when initializing the FileReader object. A Java RuntimeException will be raised, and an error message will be output to the user.

public class InputFileRead {


  private File readFile = null;
  private FileReader reader = null;
  private String inputFilePath = null;
  private final String DEFAULT_FILE_PATH = "c:\\somedirectory\\";

  public InputFileRead() {
    inputFilePath = DEFAULT_FILE_PATH;
  }

  public void setInputFile(String inputFile) {


    /* Assume appropriate validation / encoding is used and privileges / permissions are preserved */


  }

  public void readInputFile() {

    try {
      reader = new FileReader(readFile);
      ...
    } catch (RuntimeException rex) {
      System.err.println("Error: Cannot open input file in the directory " + inputFilePath);
      System.err.println("Input file has not been set, call setInputFile method before calling readInputFile");


    } catch (FileNotFoundException ex) {...}


  }

}

However, the error message output to the user contains information regarding the default directory on the local file system. This information can be exploited and may lead to unauthorized access or use of the system. Any Java RuntimeExceptions that are handled should not expose sensitive information to the user.

Example Two

In the example below, the BankManagerLoginServlet servlet class will process a login request to determine if a user is authorized to use the BankManager Web service. The doPost method will retrieve the username and password from the servlet request and will determine if the user is authorized. If the user is authorized the servlet will go to the successful login page. Otherwise, the servlet will raise a FailedLoginException and output the failed login message to the error page of the service.

public class BankManagerLoginServlet extends HttpServlet {

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    try {


      // Get username and password from login page request
      String username = request.getParameter("username");
      String password = request.getParameter("password");
      // Authenticate user
      BankManager bankMgr = new BankManager();
      boolean isAuthentic = bankMgr.authenticateUser(username, password);
      // If user is authenticated then go to successful login page
      if (isAuthentic) {
        request.setAttribute("login", new String("Login Successful."));
        getServletContext().getRequestDispatcher("/BankManagerServiceLoggedIn.jsp"). forward(request, response);
      }
      else {


        // Otherwise, raise failed login exception and output unsuccessful login message to error page
        throw new FailedLoginException("Failed Login for user " + username + " with password " + password);

      }

    } catch (FailedLoginException ex) {


      // output failed login message to error page
      request.setAttribute("error", new String("Login Error"));
      request.setAttribute("message", ex.getMessage());
      getServletContext().getRequestDispatcher("/ErrorPage.jsp").forward(request, response);

    }

  }

However, the output message generated by the FailedLoginException includes the user-supplied password. Even if the password is erroneous, it is probably close to the correct password. Since it is printed to the user's page, anybody who can see the screen display will be able to see the password. Also, if the page is cached, the password might be written to disk.

See Also