CWE-537: Java Runtime Error Message Containing Sensitive Information

Description

In many cases, an attacker can leverage the conditions that cause unhandled exception errors in order to gain unauthorized access to the system.

Potential Impact

Confidentiality

Read Application Data

Demonstrative Examples

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.

Bad

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.

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.

Bad

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.

Mitigations & Prevention

Implementation

Do not expose sensitive error information to the user.

Frequently Asked Questions

What is CWE-537?

CWE-537 (Java Runtime Error Message Containing Sensitive Information) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. In many cases, an attacker can leverage the conditions that cause unhandled exception errors in order to gain unauthorized access to the system.

How can CWE-537 be exploited?

Attackers can exploit CWE-537 (Java Runtime Error Message Containing Sensitive Information) to read application data. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-537?

Key mitigations include: Do not expose sensitive error information to the user.

What is the severity of CWE-537?

CWE-537 is classified as a Variant-level weakness (Low-Medium abstraction). Its actual severity depends on the specific context and how the weakness manifests in your application.