Nosql Injection in APIs

NoSQL injection is a code injection technique that exploits vulnerabilities in NoSQL database queries. Unlike traditional SQL injection that targets relational databases, NoSQL injection attacks manipulate the query language of document, key-value, graph, and other non-relational databases.

In API contexts, NoSQL injection occurs when user-supplied input is incorporated directly into database queries without proper sanitization. Attackers can craft malicious input to modify query logic, bypass authentication, access unauthorized data, or even execute arbitrary commands on the database server.

Common NoSQL databases affected include MongoDB, CouchDB, Cassandra, and Redis. The attack vectors vary by database type—MongoDB uses JSON-like query structures, while CouchDB uses JavaScript-based map/reduce functions. The core principle remains the same: untrusted input manipulates query execution in ways the developer didn't intend.

API endpoints that accept user input and use it to construct NoSQL queries are prime targets. Consider a typical REST API that searches for users by username:

GET /api/users?username=admin

If the backend code directly passes this parameter to a MongoDB query without validation, an attacker could inject operators like $ne (not equal) or $gt (greater than) to manipulate results.

Common attack scenarios:

• Data Access Escalation: Using operators like $ne: null or $exists: true to bypass filters and access all records
• Authentication Bypass: Crafting login requests that always evaluate to true, such as { "username": { "$ne": null }, "password": { "$ne": null } }
• Data Manipulation: Using $push, $pull, or $set operators to modify data without authorization
• Denial of Service: Crafting queries that cause excessive resource consumption or database crashes

The impact can range from unauthorized data exposure to complete database compromise, depending on the database's security configuration and the API's data access patterns.

Detecting NoSQL injection requires examining both the API code and runtime behavior. From a code perspective, look for patterns where user input is directly incorporated into database queries without proper validation or parameterization.

Key indicators include:

• Direct interpolation of request parameters into query objects
• Missing input validation for special characters and operators
• Dynamic query construction based on user input
• Lack of parameterized query interfaces

Runtime detection involves testing with malicious inputs that include NoSQL operators. For MongoDB, this might include payloads like:

{ "username": { "$ne": "" } } // bypasses equality checks
{ "$where": "this.password.length < 100" } // executes JavaScript
{ "$expr": { "$gt": [ "$accessLevel", 9 ] } } // compares field values

middleBrick's approach to NoSQL injection detection involves automated black-box scanning that tests API endpoints with NoSQL-specific payloads. The scanner identifies endpoints that accept JSON input, then systematically injects NoSQL operators to observe how the API responds. It checks for authentication bypass, data exposure, and query manipulation vulnerabilities without requiring access to source code or database credentials.

The scanner also analyzes OpenAPI specifications to understand expected input formats and validates whether the runtime behavior matches the documented contract, flagging discrepancies that might indicate injection vulnerabilities.

Preventing NoSQL injection requires a defense-in-depth approach combining input validation, parameterized queries, and principle of least privilege.

Input Validation: Validate and sanitize all user input before using it in queries. Implement strict type checking and whitelist allowed characters. For example:

function validateUsername(username) {
  const usernameRegex = /^[a-zA-Z0-9_]{3,20}$/;
  return usernameRegex.test(username);
}

// Reject invalid input early
if (!validateUsername(req.query.username)) {
  return res.status(400).json({ error: 'Invalid username format' });
}

Parameterized Queries: Use the database's built-in parameterized query interfaces instead of constructing queries dynamically. Most NoSQL drivers provide safe ways to build queries:

// Safe: parameterized query
const user = await db.collection('users').findOne({
  username: req.query.username
});

// Unsafe: direct interpolation
const user = await db.collection('users').findOne({
  username: eval(req.query.username) // NEVER do this
});

Principle of Least Privilege: Configure database users with minimal permissions. If an API only needs read access to certain collections, don't grant write or administrative privileges. This limits the blast radius if injection occurs.

ORM/ODM Libraries: Use well-maintained Object Document Mapping (ODM) libraries like Mongoose for MongoDB, which provide query builders that automatically escape inputs and prevent injection.

Security Testing: Incorporate automated security scanning into your development workflow. The middlebrick CLI tool can scan your staging APIs before deployment, and the GitHub Action can fail builds if NoSQL injection vulnerabilities are detected.

Here's a secure implementation pattern:

async function getUser(req, res) {
  const { username } = req.query;
  
  // Input validation
  if (!username || typeof username !== 'string' || username.length > 50) {
    return res.status(400).json({ error: 'Invalid username' });
  }
  
  try {
    // Parameterized query using safe ODM methods
    const user = await UserModel.findOne({ username }).exec();
    
    if (!user) {
      return res.status(404).json({ error: 'User not found' });
    }
    
    res.json(user);
  } catch (error) {
    console.error('Database error:', error);
    res.status(500).json({ error: 'Internal server error' });
  }
}

NoSQL injection vulnerabilities have led to significant data breaches and system compromises. While specific CVEs for NoSQL injection are less common than SQL injection CVEs, the attack pattern is well-documented in the security community.

In 2017, a MongoDB NoSQL injection vulnerability in a popular CMS allowed attackers to bypass authentication and access administrative functions. The vulnerability stemmed from unvalidated user input in query construction, enabling attackers to craft login requests that always returned valid user objects.

Many cryptocurrency platforms have suffered NoSQL injection attacks where attackers manipulated database queries to drain wallets or manipulate trading data. The flexible query syntax of NoSQL databases, while powerful, creates opportunities for injection when input validation is lax.

OWASP includes NoSQL injection in its API Security Top 10 under the broader category of API4: Lack of Resources & Rate Limiting, recognizing that injection attacks can lead to resource exhaustion and data exposure.

The financial impact of NoSQL injection can be severe—data breaches involving customer information, intellectual property theft, and regulatory penalties for failing to protect sensitive data. Companies have faced GDPR fines, PCI DSS violations, and loss of customer trust following NoSQL injection incidents.

Regular security scanning with tools like middleBrick helps identify these vulnerabilities before attackers can exploit them, providing actionable findings with severity ratings and remediation guidance to address the specific injection vectors discovered in your APIs.