Dangling Dns in Axum with Dynamodb

A dangling DNS record in an Axum service that uses Amazon DynamoDB can expose internal or external endpoints through inconsistent configuration or leftover references. In this scenario, an Axum application resolves a hostname (e.g., internal-db.example.com) to an IP address used by a DynamoDB endpoint or a proxy/connection wrapper. If the DNS record points to an unmanaged or deprecated address, an attacker who can influence client-side DNS resolution (e.g., via compromised DHCP, local hosts file, or a rogue resolver) may redirect the Axum application to a malicious host that mimics DynamoDB behavior.

Because Axum does not enforce strict endpoint validation for non-HTTP targets, a developer might inadvertently allow a hostname-based DynamoDB configuration to resolve to an unexpected address. This becomes a dangling DNS issue when the hostname is not actively maintained or when decommissioned infrastructure retains DNS entries. The Axum runtime continues to use the hostname from configuration, and if the application serializes requests or logs the resolved address, it might expose internal patterns or reveal connectivity details that aid lateral movement.

When combined with DynamoDB, the risk centers on how the application forms requests. If the Axum code uses a hostname to construct low-level HTTP clients that communicate with a service claiming to be DynamoDB (or a compatible interface), an attacker controlling the DNS resolution can intercept or manipulate traffic. This can lead to information disclosure if request metadata or error messages leak internal hostnames, or to injection scenarios where malformed responses are parsed by the client. The vulnerability is not in DynamoDB itself but in how Axum configuration and DNS resolution interact, especially when the hostname is treated as an implicit trust boundary.

middleBrick detects this class of issue during black-box scanning by analyzing unauthenticated attack surfaces and cross-referencing OpenAPI specifications with observed runtime behavior. For API-based integrations that reference hostnames or indirect endpoints, the scanner can identify inconsistent or overly permissive configurations that may allow unintended redirection or exposure. This is particularly relevant when the API specification includes external server URLs that are not tightly constrained, and the runtime behavior diverges from intended network boundaries.

Remediation guidance focuses on validating and hardening endpoint configuration. Use explicit IP addresses or tightly controlled domain names in Axum configuration, and avoid relying on mutable DNS records for critical service endpoints. Rotate and monitor any credentials used by the Axum-Dynamodb integration, and ensure that client builders do not trust unverified hostnames. Applying these measures reduces the attack surface associated with dangling DNS in Axum-based services that depend on DynamoDB connectivity.

To secure an Axum application that communicates with Amazon DynamoDB, configure the HTTP client with explicit, validated endpoints and avoid dynamic hostname resolution for critical services. Below is a concrete example that shows how to set up a DynamoDB client in Rust using the official AWS SDK for Rust, ensuring that the endpoint is fixed and credentials are managed safely.

use aws_config::meta::region::RegionProviderChain;
use aws_sdk_dynamodb::Client;
use std::net::SocketAddr;
use axum::Router;

async fn build_dynamodb_client() -> Client {
    let region_provider = RegionProviderChain::first_try(Some("us-east-1".parse().unwrap()))
        .or_default_provider()
        .and_then(|region| {
            if region.as_ref() == "us-east-1" {
                Some(region)
            } else {
                None
            }
        });
    let config = aws_config::from_env().region(region_provider).load().await;
    Client::new(&config)
}

#[tokio::main]
async fn main() {
    let client = build_dynamodb_client().await;
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    let app = Router::new()
        .route("/items/:id", axum::routing::get(move |id: String| {
            let client = client.clone();
            async move {
                use aws_sdk_dynamodb::types::AttributeValue;
                let output = client.get_item()
                    .table_name("my-table")
                    .key("id", AttributeValue::S(id))
                    .send()
                    .await;
                match output {
                    Ok(resp) => {
                        if let Some(item) = resp.item {
                            format!("{:?}", item)
                        } else {
                            String::from("Not found")
                        }
                    }
                    Err(e) => format!("Error: {:?}", e),
                }
            }
        }));
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}

This example avoids hostname-based endpoint resolution for DynamoDB by relying on the SDK’s default behavior and explicit region configuration. By constructing the client with a fixed region and letting the SDK use its standard endpoint resolution (which points to the official AWS service), you eliminate the risk of a dangling DNS record redirecting traffic. Do not set a custom endpoint via environment variables or builder methods unless the endpoint is under strict organizational control and validation.

For Axum routes that interact with DynamoDB, ensure that request handling does not concatenate user input into endpoint hostnames or paths that could be misinterpreted. Validate and sanitize all inputs, and use structured data formats (e.g., JSON) rather than dynamic query construction. If your architecture requires a proxy or a custom endpoint, pin the DNS name to a stable, monitored address and rotate credentials periodically. These practices align with secure integration patterns and reduce the likelihood of misconfiguration that leads to dangling DNS issues.

middleBrick’s scans can help identify whether your API specification or runtime behavior references mutable hostnames or permissive endpoint configurations. By integrating the CLI (middlebrick scan <url>) or the GitHub Action into your CI/CD pipeline, you can automatically detect risky configurations before deployment. The MCP server also allows AI coding assistants to flag insecure endpoint handling during development, supporting continuous security awareness in Axum projects that depend on DynamoDB.