Dns Cache Poisoning in Axum with Dynamodb

DNS cache poisoning is a network-layer attack where falsified DNS responses cause a resolver to associate a domain name with an incorrect IP address. In an Axum application that uses Amazon DynamoDB as a backing data store, this attack can shift trust from legitimate services to malicious ones, particularly when service endpoints are resolved at runtime and cached.

Consider an Axum service that resolves a DynamoDB endpoint (or a custom service name used to build a DynamoDB client region and endpoint) at startup or on demand and caches the result. If the application caches DNS responses without validation or uses an untrusted resolver, an attacker on the network path can inject a spoofed DNS reply. The poisoned response may point api.dynamodb.amazonaws.com or a custom domain to an attacker-controlled IP. Subsequent SDK calls to DynamoDB—such as GetItem, Query, or PutItem—are then directed to the malicious endpoint. Even though the SDK signs requests using AWS credentials, if the application logic also embeds host or bucket-based trust assumptions, the attacker may be able to observe, modify, or replay requests, especially when TLS hostname verification is not enforced or certificate validation is misconfigured.

In Axum, if route handlers resolve or derive DynamoDB client configuration from environment variables or configuration endpoints that themselves rely on DNS, a poisoned cache can redirect writes or reads. For example, an endpoint used to construct the AWS region or a custom endpoint override may be read once and cached. If that cached value is replaced by a poisoned DNS entry, the Axum handler will use the malicious endpoint for all subsequent DynamoDB operations. Because the requests are still correctly signed, the backend may accept them if the attacker also compromises or mimics the intended AWS resource naming pattern. The risk is compounded when custom certificate authorities or permissive HTTP clients are used, as they may accept responses that would otherwise fail validation.

To detect such issues, middleBrick runs 12 security checks in parallel, including input validation, authentication, and unsafe consumption analysis, alongside an LLM/AI security probe set that includes active prompt injection testing and system prompt leakage detection. While middleBrick does not fix or block, it provides prioritized findings with severity levels and remediation guidance, helping teams identify DNS-related misconfigurations before an attacker exploits them.

Leveraging the middleBrick Web Dashboard or the CLI tool (middlebrick scan <url>) can surface risky runtime behaviors and misconfigurations. For teams with continuous integration needs, the GitHub Action can add API security checks to your CI/CD pipeline and fail builds if risk scores drop below a defined threshold. The MCP Server enables scanning APIs directly from AI coding assistants within your IDE, supporting rapid feedback during development.

Remediation focuses on preventing the use of attacker-influenced values for endpoint or region resolution, enforcing strict TLS verification, and avoiding runtime DNS caching for critical service discovery.

First, resolve DynamoDB endpoints and regions at build time or via secure configuration management rather than through runtime DNS lookups. Do not derive AWS client configuration from environment variables that can be influenced by network-level attacks. Instead, pin the region and use the default AWS SDK behavior, which relies on well-known instance metadata services and trusted DNS resolvers on the host, not application-level caches.

Second, enforce strict TLS hostname verification and avoid disabling certificate validation. In Axum, ensure that any custom HTTP client used for configuration or health checks validates server certificates and hostnames. Below is an example of creating a secure HTTPS client with reqwest and rustls, which you can use for any pre‑start checks without weakening DynamoDB SDK calls:

use reqwest::Client;
use rustls::{ClientConfig, RootCertStore};
use std::sync::Arc;

async fn build_secure_client() -> Client {
    let mut root_store = RootCertStore::empty();
    // Load system roots or a specific CA bundle
    // root_store.add_server_trust_anchors(&webpki_roots::TLS_SERVER_ROOTS);
    let config = ClientConfig::builder()
        .with_safe_defaults()
        .with_root_certificates(root_store)
        .with_no_client_auth();
    let https = hyper_rustls::HttpsConnectorBuilder::new()
        .with_tls_config(Arc::new(config))
        .https_or_http()
        .enable_http1();
    Client::builder().build::<_, hyper::Body>(https))
}

Third, when initializing the DynamoDB client, prefer explicit configuration over inferred values. The AWS SDK for Rust (aws-sdk-dynamodb) obtains credentials and region from the environment or from an explicit configuration block. Do not allow runtime overrides that depend on DNS-resolved endpoints. Example of safe client initialization:

use aws_config::meta::region::RegionProviderChain;
use aws_sdk_dynamodb::Client;

async fn create_dynamodb_client() -> Client {
    // Use a static region or a secure configuration source
    let region_provider = RegionProviderChain::first_try(Some("us-east-1".parse().unwrap()))
        .or_default_provider()
        .and_then(|region| async move { Some(region) });
    let config = aws_config::from_env().region(region_provider).load().await;
    Client::new(&config)
}

Fourth, avoid caching DNS-derived values in application state. If you must cache configuration, use short TTLs and validate sources. Do not cache values that influence security boundaries, such as endpoint URLs or certificate authorities.

Finally, monitor and test using tools like middleBrick. Run scans with the CLI or automate checks via the GitHub Action to ensure risk scores remain within your acceptable threshold. The MCP Server can provide on‑the‑fly feedback during development, helping you avoid introducing insecure patterns that could be leveraged via DNS cache poisoning or related infrastructure attacks.