Dns Cache Poisoning in Fiber with Dynamodb

DNS cache poisoning can arise in a Fiber-based application that relies on Amazon DynamoDB when the service resolves internal or third-party hostnames at runtime and uses those results to influence request routing or data access. For example, a microservice might look up a DynamoDB table endpoint or a backend hostname using a custom DNS resolver, then store or query DynamoDB based on the resolved address. If the DNS responses are not validated, an attacker can inject a malicious IP into the cache, causing the application to send requests to a rogue endpoint that can read or write data to a legitimate DynamoDB resource.

In this scenario, the application might resolve a hostname such as dynamodb.us-east-1.amazonaws.com or an internal service name, and then use the resolved IP to construct AWS SDK clients or to decide which DynamoDB table to target. Because DNS cache poisoning manipulates the mapping from name to IP, the application may unknowingly interact with a malicious actor-controlled host that mimics the expected DynamoDB service. This can lead to unauthorized data access, data tampering, or injection of malicious items into DynamoDB if the application trusts the poisoned address to enforce access controls or routing logic.

Additionally, if the application logs or stores DNS-derived values in DynamoDB (for example, storing resolved endpoints for caching), poisoned entries can persist in the database and be reused across sessions. Attackers may exploit this persistence to maintain influence over application behavior. Because DynamoDB is often used as a high-integrity data store, any contamination of its inputs through DNS manipulation can result in severe security impacts, including unauthorized data exposure or injection of crafted items that exploit downstream consumers.

The risk is particularly relevant when the application uses unvalidated DNS responses to construct AWS Signature Version 4 signing contexts or to select endpoints for sensitive operations. Without strict hostname verification and secure DNS configuration, the combination of Fiber, custom DNS resolution, and DynamoDB creates a pathway for attackers to subvert expected data flows by leveraging poisoned cache entries.

To mitigate DNS cache poisoning risks in a Fiber application that interacts with DynamoDB, implement strict hostname validation, avoid reliance on runtime DNS for security-critical routing, and enforce robust AWS SDK configurations. Below are concrete remediation steps and code examples tailored to this stack.

1. Validate and pin service endpoints

Do not derive DynamoDB endpoints from DNS. Use explicit, verified endpoints and environment variables. For example, initialize the AWS SDK with a fixed endpoint URL when operating in controlled environments:

const { DynamoDB } = require("aws-sdk");

const client = new DynamoDB({
  endpoint: process.env.DYNAMODB_ENDPOINT || "https://dynamodb.us-east-1.amazonaws.com",
  region: process.env.AWS_REGION || "us-east-1",
  // Do not allow runtime overrides from untrusted sources
});

2. Harden DNS resolution when custom resolvers are necessary

If custom DNS resolution is required, use a trusted DNS library with DNSSEC validation and disable caching of untrusted responses. For example, using dns.promises with strict server selection and no cache:

const dns = require("dns").promises;
const dnsServer = "1.1.1.1"; // Use a reliable, DNSSEC-capable resolver

async function resolveHostname(hostname) {
  const result = await dns.resolve4(hostname, { server: dnsServer });
  // Optionally verify the resolved IP against an allowlist
  return result;
}

3. Enforce IAM policies and least privilege

Ensure that the IAM role or user associated with the Fiber application has permissions limited to the specific DynamoDB tables and actions required. Avoid broad permissions that could be abused if an attacker redirects traffic to a malicious host:

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

4. Verify TLS and server identity

When connecting to DynamoDB over HTTPS, ensure strict TLS verification and avoid disabling certificate checks. In environments where custom endpoints are used, explicitly set the TLS CA bundle and validate the hostname:

const https = require("https");
const fs = require("fs");

const agent = new https.Agent({
  ca: fs.readFileSync("/path/to/ca-bundle.pem"),
  checkServerIdentity: (host, cert) => {
    if (host !== "dynamodb.us-east-1.amazonaws.com") {
      throw new Error("Host mismatch");
    }
    return undefined;
  }
});

const client = new DynamoDB({ httpOptions: { agent }, region: "us-east-1" });

5. Audit and monitor interactions

Log and monitor requests to DynamoDB with a focus on unexpected endpoints or unauthorized table accesses. Correlate DNS resolution events with DynamoDB calls to detect anomalies indicative of poisoning attempts.