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Unauthorized access to files

Need​

Prevention of unauthorized access to files and functionalities

Context​

  • Usage of TypeScript for statically typed JavaScript development
  • Usage of Express for building web applications and APIs

Description​

Non compliant code​

import express from 'express';

const app = express();

app.post('/update-user', (req, res) => {
  const { userData } = req.body;

  // Vulnerable code: No server-side validation is performed on the userData

  // Update user data in the database

  res.send('User data updated successfully');
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

The vulnerability in the given code is that there is no server-side validation performed on the userData received from the request body. This means that any potentially dangerous characters or malicious input can be injected into the userData field, leading to inappropriate behavior in the application.

This vulnerability can allow an attacker to gain unauthorized access to files and functionalities, specifically in this case, the Sharepoint administrative center. By injecting certain characters or payloads, an attacker can bypass authorization checks and access files without proper authentication.

To mitigate this vulnerability, it is recommended to implement server-side validation on the userData field. This validation should ensure that only expected and safe data is accepted. Additionally, file access should be restricted to authenticated and authorized users only, to prevent unauthorized access to sensitive files.

Steps​

  • Perform server-side validation on the userData to ensure it does not contain potentially dangerous characters or malicious code
  • Implement authentication and authorization checks to restrict file access to authenticated and authorized users only

Compliant code​

import express from 'express';

const app = express();

app.post('/update-user', (req, res) => {
  const { userData } = req.body;

  // Perform server-side validation on the userData
  const sanitizedData = validateUserData(userData);

  // Update user data in the database using the sanitizedData

  res.send('User data updated successfully');
});

function validateUserData(userData: any): any {
  // Perform validation logic here to ensure userData is safe
  // You can use libraries like validator.js or implement custom validation logic

  // Return the sanitized data
  return sanitizedData;
}

// Implement authentication and authorization checks
// You can use middleware functions to check authentication and authorization

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

The fixed code addresses the vulnerability by implementing several security measures.

  1. Server-side validation: The code performs server-side validation on the userData received in the request body. The validateUserData function is responsible for performing the validation logic. It ensures that the data entered into different fields is safe and does not contain any potentially dangerous characters.

  2. Sanitization: After validating the userData, the code sanitizes the data by removing any potentially dangerous characters or content. The sanitized data is then used to update the user data in the database. The specific sanitization logic is not shown in the code snippet but should be implemented to ensure the data is safe.

  3. Authentication and authorization: The code suggests implementing authentication and authorization checks. These checks ensure that only authenticated and authorized users can access the functionality and files. The implementation of authentication and authorization is not shown in the code snippet, but it can be done using middleware functions or other authentication/authorization libraries.

By implementing these security measures, the code mitigates the vulnerability by validating and sanitizing user input, as well as restricting access to authenticated and authorized users only.

References​

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