Skip to main content

Lack of data validation - Out of range

Need​

Implementation of robust data validation and input sanitization

Context​

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

Description​

Non compliant code​

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;

public class EmployeeManagementServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        String path = request.getParameter("path");
        File file = new File(path);
        
        if (file.exists()) {
            // provide access to the file
        } else {
            // handle file not found
        }
    }
}

In the above Java Servlet code, an authenticated user can bypass restrictions by using absolute paths to access the functionalities. The doGet method is used to handle GET requests from the client.

The problem lies in this line: String path = request.getParameter("path");. Here, the application takes a "path" parameter from the request, and uses it to access a file.

This is a serious security vulnerability because the "path" parameter is not validated before use. An attacker can exploit this by providing an absolute path to a restricted file or functionality. Since there is no range or boundary check for the "path" parameter, the attacker can potentially access sensitive data or functionalities that are supposed to be restricted.

This is known as a Path Traversal vulnerability. It allows an attacker to access files and directories that are stored outside the web root folder. By manipulating variables that reference files with “dot-dot-slash (../)” sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on the file system, including application source code, configuration, and critical system files.

Steps​

  • Implement input validation to ensure that the 'path' parameter is within the allowed range of functionalities.
  • Define a whitelist of allowed paths and check if the provided 'path' parameter is in the whitelist.
  • If the 'path' parameter is not in the whitelist, handle it as an unauthorized access attempt.
  • Consider implementing role-based access control to restrict access to certain functionalities based on user roles.
  • Regularly review and update the whitelist of allowed paths to ensure it remains up to date with the application's functionality restrictions.

Compliant code​

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
import java.util.Arrays;
import java.util.List;

public class EmployeeManagementServlet extends HttpServlet {
    
    private static final List<String> WHITELIST_PATHS = Arrays.asList("/allowedPath1", "/allowedPath2", "/allowedPath3");

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        String path = request.getParameter("path");

        if (!WHITELIST_PATHS.contains(path)) {
            // handle unauthorized access attempt
            return;
        }

        File file = new File(path);
        
        if (file.exists()) {
            // provide access to the file
        } else {
            // handle file not found
        }
    }
}

The updated code includes a whitelist of allowed paths. This whitelist is a list of strings that represent the paths to which users are allowed to access. In this case, the paths are "/allowedPath1", "/allowedPath2", and "/allowedPath3".

When a GET request is made, the 'path' parameter from the request is retrieved and checked against the whitelist. If the 'path' parameter is not in the whitelist, the code handles it as an unauthorized access attempt and returns immediately, preventing any further processing of the request.

If the 'path' parameter is in the whitelist, the code proceeds to check if the file at the specified path exists. If the file exists, access is provided to the file. If the file does not exist, the code handles it as a file not found error.

This approach ensures that only authorized paths are accessible, preventing users from bypassing restrictions by using absolute paths to restricted functionalities. It also provides a centralized location for managing allowed paths, making it easier to review and update the whitelist as necessary.

References​

Last updated on