Ssrf in Dynamodb

Server-Side Request Forgery (SSRF) in DynamoDB contexts typically occurs when applications construct DynamoDB endpoint URLs dynamically based on user input, allowing attackers to redirect requests to internal services, cloud metadata endpoints, or external resources. This vulnerability is particularly dangerous in serverless architectures and microservices where DynamoDB endpoints might be exposed through application logic.

A common DynamoDB SSRF pattern emerges when developers build endpoint URLs using string concatenation. For example:

const region = req.query.region; // User-controlled
const endpoint = `https://dynamodb.${region}.amazonaws.com`;
const params = { TableName: 'Users', Key: { id: '123' } };
const response = await fetch(endpoint, { method: 'POST', body: JSON.stringify(params) });

An attacker could manipulate the region parameter to point to internal services like 169.254.169.254 (AWS metadata service) or other cloud provider endpoints, potentially exposing sensitive credentials or internal infrastructure details.

Another DynamoDB-specific SSRF vector involves misconfigured VPC endpoints. When applications use VPC endpoints for DynamoDB access, SSRF can allow attackers to reach internal services through the same endpoint mechanism. Consider this Node.js example:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB({
  endpoint: req.query.endpoint || 'https://dynamodb.us-east-1.amazonaws.com'
});

Here, an attacker could supply endpoint=http://169.254.169.254/latest/meta-data/ to access AWS instance metadata, potentially retrieving IAM credentials or other sensitive information.

Lambda functions that interact with DynamoDB are also vulnerable when they construct DynamoDB requests dynamically. A typical vulnerable pattern:

exports.handler = async (event) => {
  const tableName = event.tableName; // User-controlled
  const docClient = new AWS.DynamoDB.DocumentClient();
  
  const params = {
    TableName: tableName,
    Key: { id: event.id }
  };
  
  return await docClient.get(params).promise();
};

While this example shows table name manipulation rather than endpoint manipulation, the principle extends to any dynamic DynamoDB configuration where user input influences AWS service endpoints or configurations.

Detecting SSRF vulnerabilities in DynamoDB contexts requires both static code analysis and dynamic testing. The middleBrick scanner specifically identifies DynamoDB SSRF patterns through its comprehensive API security assessment.

middleBrick's DynamoDB SSRF detection examines code for several key patterns:

• Dynamic endpoint construction using user input
• VPC endpoint misconfigurations
• Lambda functions with user-controlled DynamoDB parameters
• CloudFormation templates with exposed DynamoDB configurations
• Infrastructure-as-Code files that allow endpoint customization

The scanner tests for SSRF by attempting to access internal services through DynamoDB endpoints. For instance, it might try to reach http://169.254.169.254 or http://localhost:8080 through your DynamoDB configuration to verify if the application properly validates and sanitizes endpoint inputs.

Here's how middleBrick reports DynamoDB SSRF findings:

{
  "severity": "high",
  "category": "SSRF",
  "finding": "DynamoDB endpoint constructed from user input allows SSRF to internal services",
  "remediation": "Use AWS SDK default endpoints and validate all user inputs",
  "affected_code": "dynamodb.js:12-18",
  "test_case": "Attempted SSRF to metadata service via DynamoDB endpoint"
}

Beyond automated scanning, manual detection should focus on:

For comprehensive DynamoDB SSRF assessment, middleBrick's black-box scanning approach tests the actual runtime behavior of your API endpoints, identifying vulnerabilities that static analysis might miss.

Remediating DynamoDB SSRF vulnerabilities requires a defense-in-depth approach that combines proper AWS SDK usage, input validation, and network security controls. Here are DynamoDB-specific remediation strategies:

1. Use Default AWS SDK Endpoints

The most effective remediation is to avoid dynamic endpoint construction entirely. Use the AWS SDK's default endpoint resolution:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB.DocumentClient();

// Correct: Let SDK handle endpoints
const params = { TableName: 'Users', Key: { id: '123' } };
const response = await dynamodb.get(params).promise();

2. Input Validation and Whitelisting

When dynamic configuration is unavoidable, implement strict validation:

const validRegions = ['us-east-1', 'us-west-2', 'eu-central-1'];
const region = req.query.region;

if (!validRegions.includes(region)) {
  throw new Error('Invalid region specified');
}

// Only allow safe endpoint construction
const endpoint = `https://dynamodb.${region}.amazonaws.com`;

3. Network-Level Controls

Implement VPC security groups and NACLs to prevent outbound access to internal services:

Resources:
  DynamoDBSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Restrict DynamoDB access
      VpcId: !Ref VPC
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          CidrIp: 0.0.0.0/0
      SecurityGroupEgress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          CidrIp: 0.0.0.0/0
        # Explicitly block metadata service
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          CidrIp: 169.254.169.254/32
          CidrIpv6: ::/0

4. IAM Role Restrictions

Limit IAM permissions to prevent SSRF exploitation:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem",
        "dynamodb:Query",
        "dynamodb:Scan"
      ],
      "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/*"
    }
  ]
}

5. Lambda Function Hardening

For serverless applications, restrict Lambda network access:

Resources:
  MyFunction:
    Type: AWS::Lambda::Function
    Properties:
      Runtime: nodejs18.x
      Handler: index.handler
      VpcConfig:
        SecurityGroupIds:
          - !Ref DynamoDBSecurityGroup
        SubnetIds:
          - !Ref PrivateSubnet
      Environment:
        Variables:
          DYNAMODB_ENDPOINT: "https://dynamodb.us-east-1.amazonaws.com"

6. Runtime Monitoring

Implement CloudWatch alarms to detect SSRF attempts:

const AWS = require('aws-sdk');
const cloudwatch = new AWS.CloudWatch();

async function monitorSSRF() {
  const params = {
    Namespace: 'AWS/DynamoDB',
    MetricName: 'HTTPCodeTarget4XX',
    Dimensions: [
      {
        Name: 'ApiName',
        Value: 'MyDynamoDBApi'
      }
    ],
    Statistic: 'Sum',
    Period: 300,
    EvaluationPeriods: 1,
    Threshold: 5,
    ComparisonOperator: 'GreaterThanThreshold'
  };
  
  return await cloudwatch.putMetricAlarm(params).promise();
}

By implementing these DynamoDB-specific remediation strategies, you can effectively prevent SSRF attacks while maintaining the functionality and performance of your DynamoDB operations.