Man In The Middle in Chi with Dynamodb

A Man In The Middle (MitM) scenario in the context of a Chi application using Amazon DynamoDB occurs when an attacker intercepts or potentially alters communication between the Chi service and DynamoDB. Because Chi routes HTTP requests and may call AWS SDK operations against DynamoDB, any weakness in transport security or identity verification can expose data in motion or enable request tampering.

In a typical Chi application, service routes invoke AWS SDK clients to get, put, or update items in a DynamoDB table. If the Chi server does not enforce strict TLS verification for outbound HTTPS calls to DynamoDB, an attacker on the network path could present a fraudulent certificate, causing the SDK to inadvertently communicate with an unintended endpoint. Similarly, if the Chi application uses IAM roles or temporary credentials that are over-permissioned, intercepted requests could be replayed with malicious payloads.

DynamoDB-specific risks arise when unauthenticated or poorly authenticated requests reach the table. For example, if a Chi endpoint constructs a GetItem or Query request using user input without strict validation, an attacker could manipulate parameters to target different keys or indexes. When combined with a weak network perimeter or misconfigured VPC endpoints, this can facilitate MitM-style manipulations where an attacker observes or modifies the parameters of DynamoDB operations initiated by Chi.

Another vector involves logging and monitoring gaps. Chi may log request parameters for debugging; if logs containing primary key values or sensitive filters are transmitted in clear text over insecure channels, an observer can harvest identifiers to craft targeted DynamoDB requests. Because DynamoDB streams and CloudWatch metrics can also be accessed via API calls, improper permissions on those downstream integrations may compound the exposure introduced by a MitM condition.

MitM in this context is less about breaking DynamoDB itself and more about ensuring the integrity and confidentiality of the path between Chi and DynamoDB. This includes enforcing TLS 1.2+ for all outbound calls, validating server certificates, applying least-privilege IAM policies to the credentials used by Chi, and validating all inputs that become DynamoDB key conditions or filter expressions.

To reduce MitM exposure when Chi interacts with DynamoDB, apply strict transport and authorization controls. Use AWS SDK defaults that enforce HTTPS and validate server certificates, and scope IAM permissions tightly to the minimum required actions and resources.

1. Enforce TLS and use AWS SDK defaults

The AWS SDK for JavaScript enforces HTTPS by default, but ensure your Chi environment does not override this with custom HTTP agents or insecure configurations. Explicitly set rejectUnauthorized behavior when creating clients, and avoid disabling certificate validation.

import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({
  region: "us-east-1",
  // Ensure HTTPS is used; default behavior is secure
  requestHandler: {
    httpsAgent: { rejectUnauthorized: true }
  }
});

2. Least-privilege IAM policy for Chi

Define an IAM policy that allows only the specific DynamoDB actions and table ARNs Chi needs. Avoid wildcard resources and actions like dynamodb:DeleteTable unless absolutely necessary.

# Example IAM policy for Chi role
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem",
        "dynamodb:PutItem",
        "dynamodb:UpdateItem"
      ],
      "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/ChiAppData"
    }
  ]
}

3. Validate inputs before constructing requests

Ensure that any user-supplied values used in key expressions or conditionals are validated and normalized. Avoid concatenating raw input into JSON condition expressions.

import { GetItemCommand, DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { unmarshall } from "@aws-sdk/util-dynamodb";

export async function getItemSafe(userId, itemId) {
  // Validate format to prevent injection via key parameters
  if (!/^[a-zA-Z0-9_-]{1,64}$/.test(userId) || !/^[a-zA-Z0-9_-]{1,64}$/.test(itemId)) {
    throw new Error("Invalid parameter format");
  }

  const client = new DynamoDBClient({ region: "us-east-1" });
  const command = new GetItemCommand({
    TableName: "ChiAppData",
    Key: {
      pk: { S: `USER#${userId}` },
      sk: { S: `ITEM#${itemId}` }
    }
  });

  const response = await client.send(command);
  return response.Item ? unmarshall(response.Item) : null;
}

4. Use AWS SDK credential providers securely

Let the SDK resolve credentials from the safest source available (e.g., ECS task role, EC2 instance profile). Avoid embedding static credentials in Chi configuration files that could be intercepted.

import { fromEnv } from "@aws-sdk/credential-providers";
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({
  credentials: fromEnv(),
  region: "us-east-1"
});

5. Enable DynamoDB encryption and verify endpoint policies

Ensure the table uses server-side encryption and that Chi’s VPC endpoints or security groups restrict traffic to known AWS endpoints. This reduces the window for interception within your network path.

# Example: describe table encryption via AWS CLI (conceptual)
aws dynamodb describe-table --table-name ChiAppData \
  --query 'Table.ServerSideEncryptionDescription'

middleBrick can assess whether your Chi endpoints that interact with DynamoDB expose an elevated attack surface. By scanning your public API endpoints, it checks for missing transport safeguards, over-permissive IAM behaviors observable via runtime tests, and input validation gaps that could enable injection or tampering. The scanner runs unauthenticated checks and, if you connect the GitHub Action or MCP Server, can integrate into CI/CD and IDE workflows to surface findings before deployment.

Use the CLI to run a quick scan: middlebrick scan https://api.example.com. For teams with more coverage needs, the Pro plan adds continuous monitoring so changes to Chi routes or DynamoDB permissions can be evaluated for security impact over time.