Dictionary Attack in Dynamodb

Dictionary attacks against DynamoDB APIs typically exploit weak authentication mechanisms or unprotected endpoints that allow credential guessing at scale. The most common manifestation occurs when applications expose DynamoDB operations without proper rate limiting or authentication controls.

A typical vulnerable pattern looks like this:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB({region: 'us-east-1'});

// Vulnerable: No rate limiting, no authentication
app.post('/api/dynamodb/scan', async (req, res) => {
  const params = {
    TableName: req.body.table,
    FilterExpression: req.body.filter || 'attribute_exists(id)'
  };
  const result = await dynamodb.scan(params).promise();
  res.json(result);
});

Attackers can automate credential guessing against exposed DynamoDB endpoints using tools that rotate through common username/password combinations or API keys. Since DynamoDB operations like ListTables, DescribeTable, and Scan return different error messages for invalid credentials versus permission denied, attackers can systematically enumerate valid credentials.

The attack surface expands when applications use IAM roles with overly permissive policies. For example:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "dynamodb:*",
      "Resource": "*"
    }
  ]
}

This wildcard policy allows attackers who obtain any valid credential to perform destructive operations like DeleteTable, UpdateItem, or BatchWriteItem across all tables.

Another DynamoDB-specific vulnerability involves timing attacks on partition key lookups. When applications expose search endpoints that query by username or email without rate limiting:

app.get('/api/users/search', async (req, res) => {
  const params = {
    TableName: 'Users',
    KeyConditionExpression: 'username = :username',
    ExpressionAttributeValues: {':username': req.query.username}
  };
  const result = await dynamodb.query(params).promise();
  res.json(result.Items);
});

Attackers can measure response times to infer valid usernames, then launch dictionary attacks on password fields or API keys associated with those accounts.

Detecting dictionary attack vulnerabilities in DynamoDB requires analyzing both the API surface and IAM configurations. middleBrick's DynamoDB-specific scanner examines endpoints for several key indicators:

Authentication Bypass Detection: The scanner tests whether DynamoDB operations are accessible without proper authentication headers or API keys. It attempts unauthenticated requests to common endpoints like /api/dynamodb/* and /api/aws/*.

Rate Limiting Analysis: middleBrick measures response times and error patterns to identify endpoints vulnerable to brute-force attacks. It looks for DynamoDB operations that don't implement exponential backoff or request throttling.

IAM Policy Analysis: When provided with AWS credentials, the scanner evaluates IAM policies for overly permissive statements. It specifically flags wildcard actions like dynamodb:* and resources like *.

Exposed Metadata Endpoints: The scanner tests for exposed DynamoDB metadata endpoints that could reveal table structures, partition keys, or attribute names that aid credential guessing.

Here's how you might use middleBrick's CLI to scan a DynamoDB-backed API:

npx middlebrick scan https://api.example.com/v1/users

The scanner runs 12 security checks in parallel, including authentication bypass testing and input validation analysis specific to DynamoDB's JSON-based query language.

For applications using AWS SDK directly, middleBrick analyzes the client configuration:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB({
  region: 'us-east-1',
  // Scanner checks if credentials are hardcoded or exposed
  accessKeyId: process.env.AWS_ACCESS_KEY_ID,
  secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY
});

The scanner flags hardcoded credentials, missing encryption at rest, and exposed AWS access keys in client-side JavaScript.

Securing DynamoDB against dictionary attacks requires implementing defense-in-depth strategies. Start with proper IAM policy configuration:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem",
        "dynamodb:PutItem",
        "dynamodb:UpdateItem",
        "dynamodb:DeleteItem"
      ],
      "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Users"
    }
  ]
}

Never use wildcard permissions. Instead, specify exact table ARNs and required actions.

Implement API-level rate limiting using DynamoDB's native features:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB({region: 'us-east-1'});

async function safeGetItem(tableName, key) {
  try {
    // Implement client-side throttling
    const params = {
      TableName: tableName,
      Key: key,
      ReturnConsumedCapacity: 'TOTAL'
    };
    
    // Check for throttling before making request
    const describeParams = {
      TableName: tableName
    };
    const tableInfo = await dynamodb.describeTable(describeParams).promise();
    
    // Implement custom rate limiting based on table capacity
    const consumedCapacity = tableInfo.Table.ProvisionedThroughput.ReadCapacityUnits;
    if (consumedCapacity > 80) {
      throw new Error('Rate limit exceeded');
    }
    
    return await dynamodb.getItem(params).promise();
  } catch (error) {
    // Implement exponential backoff
    if (error.code === 'ProvisionedThroughputExceededException') {
      await new Promise(resolve => setTimeout(resolve, 100));
      return await safeGetItem(tableName, key);
    }
    throw error;
  }
}

Add authentication middleware to all DynamoDB operations:

const jwt = require('jsonwebtoken');
const AWS = require('aws-sdk');

const dynamodb = new AWS.DynamoDB({region: 'us-east-1'});

function authenticate(req, res, next) {
  const authHeader = req.headers.authorization;
  if (!authHeader || !authHeader.startsWith('Bearer ')) {
    return res.status(401).json({error: 'Missing token'});
  }
  
  const token = authHeader.substring(7);
  jwt.verify(token, process.env.JWT_SECRET, (err, user) => {
    if (err) {
      return res.status(401).json({error: 'Invalid token'});
    }
    req.user = user;
    next();
  });
}

// Apply authentication to all DynamoDB routes
app.use('/api/dynamodb/*', authenticate);

For enhanced security, implement API key rotation and monitoring:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB({region: 'us-east-1'});

async function rotateApiKey(userId) {
  const newKey = generateSecureApiKey();
  
  // Store new key with limited validity
  const params = {
    TableName: 'ApiKeys',
    Item: {
      userId: {S: userId},
      apiKey: {S: newKey},
      createdAt: {S: new Date().toISOString()},
      expiresAt: {S: new Date(Date.now() + 24*60*60*1000).toISOString()}
    }
  };
  
  await dynamodb.putItem(params).promise();
  return newKey;
}

Enable DynamoDB's built-in monitoring and alerting for suspicious patterns:

const AWS = require('aws-sdk');
const cloudwatch = new AWS.CloudWatch({region: 'us-east-1'});

async function setupAlarms(tableName) {
  const params = {
    AlarmName: `${tableName}-HighErrorRate`,
    ComparisonOperator: 'GreaterThanThreshold',
    EvaluationPeriods: 1,
    MetricName: 'SuccessfulRequestLatency',
    Namespace: 'AWS/DynamoDB',
    Period: 300,
    Statistic: 'Average',
    Threshold: 500.0,
    AlarmActions: ['arn:aws:sns:us-east-1:123456789012:SecurityAlerts']
  };
  
  await cloudwatch.putMetricAlarm(params).promise();
}