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Insecure object reference - Corporate information

Need​

Secure object reference management

Context​

  • Usage of C# for developing robust and efficient applications
  • Usage of Microsoft.AspNetCore.Mvc for building web applications using the ASP.NET Core MVC framework
  • Usage of Microsoft.AspNetCore.Http for handling HTTP requests and responses in ASP.NET Core applications
  • Usage of System.IO for input/output operations in .NET development
  • Usage of System.Collections.Generic for working with generic collections in .NET
  • Usage of OfficeOpenXml for working with Excel files in Node.js

Description​

Non compliant code​

[HttpPost]
public async Task<IActionResult> UploadExcelFile(IFormFile file)
{
    var employees = new List<Employee>();
    var payrollNumber = Request.Form["payrollNumber"].ToString();

    using (var stream = new MemoryStream())
    {
        await file.CopyToAsync(stream);
        using (var package = new ExcelPackage(stream))
        {
            ExcelWorksheet worksheet = package.Workbook.Worksheets[0];
            for (int i = worksheet.Dimension.Start.Row + 1; i <= worksheet.Dimension.End.Row; i++)
            {
                employees.Add(new Employee
                {
                    PayrollNumber = payrollNumber,
                    Name = worksheet.Cells[i, 1].Value.ToString().Trim(),
                    Position = worksheet.Cells[i, 2].Value.ToString().Trim(),
                    Salary = decimal.Parse(worksheet.Cells[i, 3].Value.ToString().Trim())
                });
            }
        }
    }

    _context.Employees.AddRange(employees);
    await _context.SaveChangesAsync();

    return Ok();
}

This vulnerable code is an HTTP POST method in an ASP.NET Core controller that accepts an Excel file and a payroll number from the request. It reads the Excel file and creates a list of Employee objects from the data in the file. Each Employee object is associated with the payroll number provided in the request.

The vulnerability lies in the fact that the payroll number, which is used as a company identifier, is taken directly from the request without any checks on whether the user making the request has the necessary permissions to modify data associated with that payroll number. This means that an attacker can upload an Excel file with arbitrary employee data and associate it with any company by providing the company's payroll number in the request. This can lead to unauthorized modification of employee data.

The code does not validate the user's permissions to make changes to the company identified by the payroll number, and it does not validate the integrity of the employee data in the Excel file. This makes it an insecure direct object reference (IDOR) vulnerability, which is a type of access control vulnerability.

Steps​

  • Implement authentication and authorization mechanisms to ensure that only authorized users can access and modify employee information.
  • Validate the payrollNumber parameter to ensure that the user has permission to modify employees of the specified company.
  • Implement input validation to prevent malicious data from being uploaded and processed.
  • Use parameterized queries or stored procedures to prevent SQL injection attacks.
  • Implement proper error handling and logging to detect and respond to any potential security incidents.
  • Regularly update and patch the application and its dependencies to address any known security vulnerabilities.
  • Conduct regular security assessments and penetration testing to identify and address any potential vulnerabilities.

Compliant code​

[HttpPost]
[Authorize] // Add authorization attribute
public async Task<IActionResult> UploadExcelFile(IFormFile file, [FromServices] IAuthorizationService authorizationService)
{
    var employees = new List<Employee>();
    var payrollNumber = Request.Form["payrollNumber"].ToString();

    // Check if the user has permission to modify the specified company's employees
    var isAuthorized = await authorizationService.AuthorizeAsync(User, payrollNumber, "ModifyEmployees");
    if (!isAuthorized.Succeeded)
    {
        return Forbid();
    }

    using (var stream = new MemoryStream())
    {
        await file.CopyToAsync(stream);
        using (var package = new ExcelPackage(stream))
        {
            ExcelWorksheet worksheet = package.Workbook.Worksheets[0];
            for (int i = worksheet.Dimension.Start.Row + 1; i <= worksheet.Dimension.End.Row; i++)
            {
                employees.Add(new Employee
                {
                    PayrollNumber = payrollNumber,
                    Name = worksheet.Cells[i, 1].Value.ToString().Trim(),
                    Position = worksheet.Cells[i, 2].Value.ToString().Trim(),
                    Salary = decimal.Parse(worksheet.Cells[i, 3].Value.ToString().Trim())
                });
            }
        }
    }

    _context.Employees.AddRange(employees);
    await _context.SaveChangesAsync();

    return Ok();
}

The updated code now includes an [Authorize] attribute to ensure that only authenticated users can access the UploadExcelFile method.

In addition, we've added an IAuthorizationService parameter to the method, which is used to check if the authenticated user has permission to modify the employees of the company specified by the payrollNumber parameter. If the user does not have the necessary permission, the method returns a Forbid result, which translates to a 403 Forbidden HTTP status code.

This way, we ensure that only authorized users can modify the employee data, and they can only modify data for companies they have permission to access. This effectively mitigates the insecure object reference vulnerability.

Remember to define the "ModifyEmployees" policy in your Startup.cs file or wherever you configure your authorization policies. The policy should check if the user has permission to modify the employees of the specified company.

Also, remember to validate the input file and the data it contains to prevent malicious data from being uploaded and processed. This could be done in a separate method before processing the file.

Finally, use parameterized queries or Entity Framework's built-in methods (like we do here with AddRange and SaveChangesAsync) to interact with the database and prevent SQL injection attacks.

References​

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