NoSQL injection

What is NoSQL databases?

NoSQL databases store and retrieve data in a format other than traditional SQL relational tables. They are designed to handle large volumes of unstructured or semi-structured data. As such they typically have fewer relational constraints and consistency checks than SQL, and claim significant benefits in terms of scalability, flexibility, and performance.

Like SQL databases, users interact with data in NoSQL databases using queries that are passed by the application to the database. However, different NoSQL databases use a wide range of query languages instead of a universal standard like SQL (Structured Query Language). This may be a custom query language or a common language like XML or JSON.

A few examples of NoSQL databases include:

1. MongoDB, a popular open-source NoSQL database supported

2. Redis, an in-memory key-value store often used for caching data

3. Elasticsearch, a commonly used NoSQL database for at-scale and complex search operations

4. Apache CouchDB, a popular open-source NoSQL database with native REST HTTP API support

5. Cloudflare KV or Amazon DynamoDB, both well-known serverless key-value storage options

Summary

NoSQL injection is a vulnerability where an attacker is able to interfere with the queries that an application makes to a NoSQL database. NoSQL injection may enable an attacker to:

• Bypass authentication or protection mechanisms.

• Extract or edit data.

• Cause a denial of service.

• Execute code on the server.

NoSQL databases store and retrieve data in a format other than traditional SQL relational tables. They use a wide range of query languages instead of a universal standard like SQL, and have fewer relational constraints.

How NoSQL Injection Differs from Traditional SQL Injection

Both SQL Injection (SQLi) and NoSQL Injection (NoSQLi) are techniques used by attackers to bypass security checks, usually to log in without valid credentials or access unauthorized data. However, they differ in how the backend processes their input.

Traditional SQL Injection

SQLi targets relational databases like MySQL, PostgreSQL, or SQL Server that use SQL (Structured Query Language).

Imagine a website login form where the backend builds this SQL query:

SELECT * FROM users WHERE username = 'alice' AND password = 'password123';

If the input is not sanitized, an attacker can input the following into the username field:

alice' OR 1=1 --

This transforms the SQL query into:

SELECT * FROM users WHERE username = 'alice' OR 1=1 -- ' AND password = 'password123';

Since OR 1=1 always returns true, and -- comments out the rest, the attacker gains access without needing the correct password.

NoSQL Injection

NoSQLi targets databases like MongoDB, which use a different format—usually JSON—for querying data.

A typical MongoDB login check might look like this:

db.users.findOne({ username: "alice", password: "password123" })

If the server accepts raw JSON and doesn’t validate the input, an attacker could send this:

{
  "username": "alice",
  "password": { "$or": [ {}, { "$ne": null } ] }
}

This uses the $or and $ne (not equal) operators to trick the database into accepting almost any password, because one part of the condition will always be true.

Identifying NoSQL Injection Vulnerabilities

To spot NoSQL injection vulnerabilities, you need to test input fields and see how the database reacts to unexpected input. Here’s how to do it:

Test Input Fields: Look for places where users can input data, such as forms, URL parameters, and API requests.

Inject Special Characters: Try adding special characters that could break the query or trigger the database to behave differently. Common ones include:

$, {, }, \, ", ', ;, and %00 (null byte)

Observe Changes: Watch for changes in the server’s response, such as:

• Content length changing.

• Unexpected status codes (like 500 errors).

• Strange response headers.

Since NoSQL databases like MongoDB or Firebase have different query languages, make sure you understand the syntax of the specific database you're working with.

Types of NoSQL injection

There are two different types of NoSQL injection:

• Syntax injection - This occurs when you can break the NoSQL query syntax, enabling you to inject your own payload. The methodology is similar to that used in SQL injection. However the nature of the attack varies significantly, as NoSQL databases use a range of query languages, types of query syntax, and different data structures.

• Operator injection - This occurs when you can use NoSQL query operators to manipulate queries.

Conclusion

NoSQL injection is a critical vulnerability that can give attackers access to sensitive data or even allow them to execute malicious commands on your server. Unlike traditional SQL injection, which exploits the structure of SQL queries, NoSQL injection takes advantage of the unique query systems used by NoSQL databases. With applications increasingly relying on NoSQL databases like MongoDB, Redis, and others, understanding how NoSQL injection works and how to secure against it is more important than ever.

In the next part of this blog, we’ll break down the different types of NoSQL injection attacks in detail. We'll discuss how syntax injection and operator injection work, provide clear examples of each, and give you actionable tips for securing your NoSQL databases.

Stay tuned for more practical advice on preventing NoSQL injection!