Command Injection in Dynamodb

Command injection in Dynamodb contexts typically occurs when user input is improperly handled in the construction of DynamoDB API requests or when database operations are dynamically constructed from untrusted input. Unlike traditional command injection where system commands are executed, DynamoDB command injection involves malicious manipulation of database operations, item attributes, or query parameters.

The most common DynamoDB command injection patterns include:

• Expression Attribute Injection - Malicious actors inject additional conditions or modify existing ones in ExpressionAttributeValues or ExpressionAttributeNames
• Key Condition Manipulation - Attackers alter partition key or sort key values to access unauthorized data
• Update Expression Tampering - Malicious modification of UpdateExpression to change unintended attributes
• Projection Expression Abuse - Exploitation of ProjectionExpression to access sensitive attributes

Consider this vulnerable DynamoDB operation:

const dynamodb = new AWS.DynamoDB.DocumentClient();
const userId = req.query.userId;
const query = req.query.query;

const params = {
  TableName: 'Users',
  KeyConditionExpression: 'userId = :userId AND begins_with(attribute, :query)',
  ExpressionAttributeValues: {
    ':userId': userId,
    ':query': query
  }
};

dynamodb.query(params, (err, data) => {
  // Process results
});

An attacker could manipulate the query parameter to include DynamoDB expression syntax, potentially bypassing intended filters or accessing unauthorized data. For example, setting query=foo' OR begins_with(attribute, 'malicious would modify the KeyConditionExpression behavior.

Another common pattern involves UpdateExpression manipulation:

const updateParams = {
  TableName: 'Orders',
  Key: { orderId: req.body.orderId },
  UpdateExpression: 'set status = :status',
  ExpressionAttributeValues: {
    ':status': req.body.status
  }
};

dynamodb.update(updateParams, callback);

If status is not properly validated, an attacker could inject additional operations like ':status = "shipped", adminNotes = :notes' to modify unintended attributes.

Detecting command injection in DynamoDB requires both static analysis of code patterns and dynamic testing of runtime behavior. The key indicators include:

Static Analysis Indicators

Dynamic Testing Approaches

middleBrick's DynamoDB-specific scanning tests for command injection by:

• Analyzing the unauthenticated attack surface of DynamoDB endpoints
• Testing for expression attribute injection vulnerabilities
• Checking for improper handling of partition and sort keys
• Scanning for excessive data exposure through projection expressions
• Verifying proper authentication and authorization controls

The scanner evaluates 12 security checks in parallel, including:

{
  "dynamodb_checks": {
    "expression_injection": true,
    "key_manipulation": true,
    "update_expression_tampering": true,
    "projection_expression_abuse": true,
    "authentication_bypass": true
  }
}

middleBrick's black-box scanning approach tests the actual runtime behavior without requiring credentials or configuration. The scanner attempts to manipulate DynamoDB API calls to identify command injection vulnerabilities, providing specific findings with severity levels and remediation guidance.

For comprehensive security assessment, middleBrick also analyzes OpenAPI/Swagger specifications to ensure DynamoDB operations are properly documented and secured, cross-referencing spec definitions with runtime findings to identify discrepancies.

Securing DynamoDB operations against command injection requires a defense-in-depth approach combining input validation, parameterized queries, and proper access controls. Here are DynamoDB-specific remediation strategies:

1. Input Validation and Sanitization

function validateUserId(userId) {
  const userIdPattern = /^[a-zA-Z0-9_-]{3,50}$/;
  if (!userIdPattern.test(userId)) {
    throw new Error('Invalid userId format');
  }
  return userId;
}

function sanitizeQuery(query) {
  const sanitized = query.replace(/[";'()]/g, '');
  if (sanitized.length > 100) {
    throw new Error('Query too long');
  }
  return sanitized;
}

// Secure usage
const params = {
  TableName: 'Users',
  KeyConditionExpression: 'userId = :userId AND begins_with(attribute, :query)',
  ExpressionAttributeValues: {
    ':userId': validateUserId(req.query.userId),
    ':query': sanitizeQuery(req.query.query)
  }
};

2. Use Parameterized Expressions

Always use parameterized expressions rather than string concatenation:

// Vulnerable
const params = {
  UpdateExpression: `set status = "${req.body.status}"`
};

// Secure
const params = {
  UpdateExpression: 'set status = :status',
  ExpressionAttributeValues: {
    ':status': req.body.status
  }
};

3. Implement IAM Least Privilege

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem",
        "dynamodb:Query",
        "dynamodb:Scan"
      ],
      "Resource": "arn:aws:dynamodb:region:account-id:table/Users"
    }
  ]
}

4. Use DynamoDB Mapper Libraries

High-level libraries provide built-in protection:

@DynamoDBTable(tableName = "Users")
public class User {
  @DynamoDBHashKey(attributeName = "userId")
  private String userId;
  
  @DynamoDBAttribute(attributeName = "status")
  private String status;
  
  // Getters and setters
}

// Usage with mapper provides type safety
DynamoDBMapper mapper = new DynamoDBMapper(dynamo);
User user = mapper.load(User.class, userId);
user.setStatus(newStatus);
mapper.save(user);

5. Implement Request Validation Middleware

const validateDynamoParams = (params) => {
  const validOperators = ['=', '>', '<', 'BETWEEN', 'IN', 'begins_with'];
  
  Object.entries(params.ExpressionAttributeValues || {}).forEach(([key, value]) => {
    if (typeof value !== 'string' && typeof value !== 'number') {
      throw new Error(`Invalid value type for ${key}`);
    }
  });
  
  // Additional validation for expressions
  if (params.KeyConditionExpression) {
    // Validate expression syntax
  }
  
  return params;
};

6. Monitor and Alert

Implement monitoring for suspicious patterns:

const monitorDynamoCalls = (params) => {
  const suspiciousPatterns = [
    /OR/i,
    /AND/i,
    /;/,
    /--/
  ];
  
  const expression = params.UpdateExpression || params.KeyConditionExpression;
  if (expression && suspiciousPatterns.some(pattern => pattern.test(expression))) {
    console.warn('Suspicious DynamoDB expression detected:', expression);
    // Alert or block
  }
};