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Lack of data validation - Content Spoofing

Need​

Implementation of robust data validation and authentication mechanisms

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance improvements.
  • Usage of javax.servlet-api for developing Java web applications with Servlet technology

Description​

Non compliant code​

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;

public class FileUploadServlet extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String filePath = request.getParameter("file_path");
        File file = new File(filePath);

        if (!file.exists()) {
            file.createNewFile();
        }

        // ... Code for file upload here ...
    }
}

This Java Servlet is used to handle file uploads. When a POST request is made to this servlet, it will attempt to create a new file at the path specified by the "file_path" request parameter.

The vulnerability lies in the fact that there is no validation to check if a file already exists at the specified path. This means that an attacker can specify the path of a file that has already been uploaded by another user, and the servlet will simply create a new file at that path, effectively overwriting the existing file.

Furthermore, there is no authentication or authorization checks in this servlet. This means that any user, even those who are not logged in, can make a POST request to this servlet and upload a file. This is a serious security risk as it allows an unauthorized attacker to upload malicious files to the server.

To fix this vulnerability, we need to add checks to ensure that a file does not already exist at the specified path before creating a new file. We also need to add authentication and authorization checks to ensure that only authorized users can upload files.

Steps​

  • Implement authentication and authorization mechanisms to ensure that only authorized users can upload files.
  • Validate the file path provided by the user to prevent directory traversal attacks.
  • Check if the file already exists before creating a new file to prevent overwriting existing files.
  • Implement file type validation to ensure that only allowed file types can be uploaded.
  • Implement file size validation to prevent uploading excessively large files.
  • Consider implementing secure file storage mechanisms to protect the uploaded files from unauthorized access.

Compliant code​

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;

public class FileUploadServlet extends HttpServlet {

    private static final long MAX_FILE_SIZE = 1024 * 1024 * 10; // 10MB
    private static final List<String> ALLOWED_FILE_TYPES = Arrays.asList("jpg", "png", "pdf"); // Allowed file types

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Authentication and Authorization code here...

        String filePath = request.getParameter("file_path");

        // Validate file path to prevent directory traversal attacks
        if (!isValidPath(filePath)) {
            throw new ServletException("Invalid file path");
        }

        File file = new File(filePath);

        // Check if file already exists
        if (file.exists()) {
            throw new ServletException("File already exists");
        }

        // Validate file type
        String fileType = getFileExtension(file);
        if (!ALLOWED_FILE_TYPES.contains(fileType)) {
            throw new ServletException("Invalid file type");
        }

        // Validate file size
        if (file.length() > MAX_FILE_SIZE) {
            throw new ServletException("File size exceeds limit");
        }

        file.createNewFile();

        // ... Code for file upload here ...
    }

    private boolean isValidPath(String filePath) {
        // Implement path validation logic here...
    }

    private String getFileExtension(File file) {
        String fileName = file.getName();
        int dotIndex = fileName.lastIndexOf('.');
        return (dotIndex == -1) ? "" : fileName.substring(dotIndex + 1);
    }
}

The updated code includes several security measures to prevent unauthorized file uploads and content spoofing:

  1. Authentication and Authorization: The code should include mechanisms to ensure that only authorized users can upload files. This part is not implemented in the provided code and should be added according to the specific authentication and authorization methods used in the application.

  2. File Path Validation: The isValidPath method should be implemented to validate the file path provided by the user and prevent directory traversal attacks.

  3. File Existence Check: The code checks if the file already exists before creating a new one to prevent overwriting existing files.

  4. File Type Validation: The code checks the file extension against a list of allowed file types to prevent the upload of potentially dangerous files.

  5. File Size Validation: The code checks the file size against a maximum limit to prevent uploading excessively large files that could cause performance issues or be used in denial-of-service attacks.

  6. Secure File Storage: Although not shown in the code, consider implementing secure file storage mechanisms to protect the uploaded files from unauthorized access. This could include storing the files in a secure location, encrypting the files, or using a secure file storage service.

References​

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