Externally-Generated 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

The following servlet code does not catch runtime exceptions, meaning that if such an exception were to occur, the container may display potentially dangerous information (such as a full stack trace).

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

  String username = request.getParameter("username");

  // May cause unchecked NullPointerException.
  if (username.length() < 10) {
    ...
  }

}

Example Two

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.

See Also