Mass Assignment 101

Impart Security
Published on
April 16, 2024
Read time
Impart Security
April 16, 2024

In this blog post, we'll take a look at what mass assignment attacks are, how they work, and why it's important for businesses and organizations to be aware of them. We'll also discuss some best practices for preventing mass assignment attacks and protecting your API from this type of threat. By understanding mass assignment attacks and taking steps to prevent them, you can help to keep your API and your business secure.

What is a Mass Assignment attack?

A mass assignment attack is a type of security vulnerability that occurs when an attacker is able to modify the values of multiple object's properties by passing them in as part of an HTTP request.  This is typically done in bulk where multiple objects are changed at once using attack automation tooling.  

This can allow the attacker to set the values of sensitive properties, such as passwords or security permissions, without the proper authorization which can result in significant risk exposure, exfiltration of data, or data loss.

Mass assignment attacks are often made possible by insufficient input validation or the lack of an object-level access control mechanism. For example, if an application allows users to submit an HTTP request with a JSON or XML payload that includes all of the properties of an object, an attacker may be able to manipulate the values of these properties in order to gain unauthorized access or permissions.

Here's an example of an API vulnerable to Mass Assignment attack:

@app.route('/users', methods=['POST'])
def create_user():
 user_data = request.json
 user = User(user_data)
 return jsonify(user.to_dict())

In this example, the create_user endpoint accepts a JSON object containing the user's username and password. It then creates a User object using the data from the request and saves it to the database.

However, this code is vulnerable to a mass assignment attack, because it allows an attacker to specify arbitrary attributes for the User object by including them in the JSON object that is sent in the request. For example, an attacker could add an admin attribute to the JSON object, and the User object would be created with that attribute set to true, giving the attacker administrator access to the system.

Why you need to know about Mass Assignment

Mass assignment attacks are a type of vulnerability that can affect APIs, and are a serious concern for businesses and organizations. These attacks can allow attackers to gain unauthorized access to sensitive data, or to take control of the API and perform actions that they should not be able to. This can have serious consequences for the business, such as data breaches, loss of customer trust, and financial losses.

In addition to the direct impact on the business, mass assignment attacks can also have indirect effects. For example, if an attacker is able to take control of an API, they may be able to use it to launch other attacks, such as denial of service attacks or injection attacks. This can have even wider-reaching consequences for the business, and can cause significant damage to the organization's reputation and bottom line.

How to prevent mass assignment attacks

To prevent mass assignment attacks, it is important to properly validate user input and implement object-level access controls to ensure that only authorized users can modify the values of sensitive properties. This can include restricting the properties that can be modified in an HTTP request, as well as verifying the user's permissions before allowing them to make any changes.

One way to prevent your API from being attacked by a mass assignment attack is to validate and sanitize your API inputs.  use an input validation and sanitization tool. This approach can help you ensure that only authorized parameters are accepted by your API, and that any potentially harmful input is sanitized or rejected.  However, this type of solution can be difficult to implement in real life and is best supplemented with other approaches as well.

Another way to prevent mass assignment attacks is to use an API runtime protection tool that provides built-in protection against mass assignment attacks. An runtime protection tool acts as a layer of protection between your API and the outside world, and can help prevent unauthorized or malicious requests from reaching your API.  Unfortunately, most runtime protection tools (like WAFs or API Gateways) lack the intelligence to recognize mass assignment attacks.  

Another way to prevent mass assignment attacks is to use a whitelist-based approach to parameter validation. This means only allowing specific, authorized parameters to be accepted by your API, and rejecting any other input.  This approach is sometimes referred to as implementing a positive security model.

Additionally, you can use a combination of these approaches to provide a more robust defense against mass assignment attacks. By using input validation and sanitization tools, a runtime protection solution, and a whitelist-based approach, you can help protect your API from mass assignment attacks and other threats.  Bringing all of these approaches together in a seamless solution is the best path forward and what we're building at Impart Security.

Overall, it's important for businesses and organizations to be aware of mass assignment attacks and to take steps to prevent them. By understanding this type of attack and implementing appropriate safeguards, you can help to keep your API and your business secure.  

Please contact us if you'd like to learn more or try our closed beta!

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