Secure handling of corporate information and prevention of unauthorized access and modification
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;
public class EmployeeUploadServlet extends HttpServlet {
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Part filePart = request.getPart("file"); // Retrieves
InputStream fileContent = filePart.getInputStream();
Workbook workbook = new XSSFWorkbook(fileContent);
Sheet sheet = workbook.getSheetAt(0);
Iterator rowIterator = sheet.iterator();
while (rowIterator.hasNext()) {
Row row = rowIterator.next();
String payrollNumber = row.getCell(0).getStringCellValue();
String employeeName = row.getCell(1).getStringCellValue();
String employeeAddress = row.getCell(2).getStringCellValue();
// Assume updateEmployeeInfo is a method to update employee info in database
updateEmployeeInfo(payrollNumber, employeeName, employeeAddress);
}
workbook.close();
fileContent.close();
}
private void updateEmployeeInfo(String payrollNumber, String employeeName, String employeeAddress) {
// Update employee info in database
}
}
The above code represents a servlet that handles POST requests to upload an Excel file. The file is expected to contain employee information that is then used to update the database.
The vulnerability lies in the fact that there is no validation of the
payrollNumber that is extracted from the Excel file. This means that an attacker can manipulate the
payrollNumber in the Excel file to target a company they do not have access to.
The
doPost method retrieves the file from the request, reads the Excel file and iterates over the rows. For each row, it extracts the
payrollNumber,
employeeName, and
employeeAddress, and passes them to the
updateEmployeeInfo method.
The
updateEmployeeInfo method then updates the employee information in the database. However, since there is no check to ensure that the
payrollNumber belongs to the company of the authenticated user, this can lead to unauthorized modification of data.
In this way, an attacker can upload an Excel file with arbitrary
payrollNumber, and the server will process this file and update the information of the company associated with the
payrollNumber, even if the attacker doesn't have the authority to do so. This is a classic case of Insecure Direct Object Reference (IDOR) vulnerability.
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;
public class EmployeeUploadServlet extends HttpServlet {
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpSession session = request.getSession();
User user = (User) session.getAttribute("user");
if (user == null || !user.hasPermission("upload")) {
response.sendError(HttpServletResponse.SC_FORBIDDEN, "You do not have permission to upload files.");
return;
}
Part filePart = request.getPart("file"); // Retrieves
if (!filePart.getContentType().equals("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")) {
response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Invalid file type.");
return;
}
InputStream fileContent = filePart.getInputStream();
Workbook workbook = new XSSFWorkbook(fileContent);
Sheet sheet = workbook.getSheetAt(0);
Iterator rowIterator = sheet.iterator();
while (rowIterator.hasNext()) {
Row row = rowIterator.next();
String payrollNumber = row.getCell(0).getStringCellValue();
String employeeName = row.getCell(1).getStringCellValue();
String employeeAddress = row.getCell(2).getStringCellValue();
if (!user.hasPermission("modify", payrollNumber)) {
response.sendError(HttpServletResponse.SC_FORBIDDEN, "You do not have permission to modify this employee.");
continue;
}
// Assume updateEmployeeInfo is a method to update employee info in database
updateEmployeeInfo(payrollNumber, employeeName, employeeAddress);
}
workbook.close();
fileContent.close();
}
private void updateEmployeeInfo(String payrollNumber, String employeeName, String employeeAddress) {
// Update employee info in database
}
}
The updated code now includes several security measures to prevent unauthorized access and modification of employee information.
1. Authentication and Authorization: The code now checks if the user is logged in and has the necessary permissions to upload files and modify employee information. If the user is not authenticated or does not have the necessary permissions, the server responds with a 403 Forbidden error.
2. File Type Validation: The code now checks the content type of the uploaded file to ensure that it is an Excel spreadsheet. If the file is not an Excel spreadsheet, the server responds with a 400 Bad Request error.
3. Access Control: The code now checks if the user has the necessary permissions to modify each employee's information based on their payroll number. If the user does not have the necessary permissions, the server responds with a 403 Forbidden error for that specific employee and continues processing the rest of the file.
4. Secure Object References: The code now uses secure object references by checking the user's permissions for each payroll number, rather than blindly trusting the payroll numbers provided in the uploaded file.
5. Error Handling and Logging: The code now includes proper error handling and sends appropriate HTTP response codes when an error occurs. This allows for better logging and detection of potential security incidents or unauthorized access attempts.
6. Regular Updates and Security Assessments: While not shown in the code, it is recommended to regularly update and patch any third-party libraries or dependencies used in the code, as well as conduct regular security assessments and penetration testing to identify and address any potential vulnerabilities.