Man In The Middle in Axum with Dynamodb

A Man In The Middle (MitM) risk arises in an Axum service that communicates with DynamoDB over unencrypted or improperly validated connections. In this stack, the server-side Axum application acts as the client to DynamoDB; if TLS is not enforced or certificate validation is skipped, an attacker who can influence network routing may intercept or alter traffic between the service and the database. This exposes credentials, IAM tokens embedded in requests, and the data flowing to and from DynamoDB. Because DynamoDB typically requires long-lived credentials for signing requests, intercepted metadata or session tokens can allow an attacker to make unauthorized calls.

Additionally, if the Axum application deserializes DynamoDB responses without strict schema validation, an attacker who can position themselves on the path may inject malicious or malformed data that exploits deserialization logic. This can lead to injection-like behaviors or logic bypass even though DynamoDB itself does not execute code. The risk is compounded when debugging endpoints or health routes in Axum inadvertently expose raw requests or responses containing AWS signatures, giving an attacker insight into valid signing keys or regions.

Using middleBrick to scan your API surface can highlight missing transport protections and improper credential handling in the flow between Axum and DynamoDB. While middleBrick does not fix these issues, it provides prioritized findings with remediation guidance to help you address the attack path before exposure leads to data leakage or privilege escalation.

To reduce MitM risk between Axum and DynamoDB, enforce TLS with strict certificate validation and avoid passing sensitive data in URLs or logs. Use the official AWS SDK for Rust (aws-sdk-dynamodb), which defaults to SigV4 signing over HTTPS and respects system or custom certificate authorities when configured via the AWS config loader.

Example: Configure the DynamoDB client with explicit region and HTTPS endpoint, and ensure the AWS SDK uses the system certificate store. Do not disable certificate validation.

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

async fn build_dynamodb_client() -> Client {
    let region_provider = RegionProviderChain::first_try(Some("us-east-1".parse().unwrap()))
        .or_default_provider()
        .and_then(|region| region);
    let config = aws_config::from_env().region(region_provider).load().await;
    Client::new(&config)
}

Example: In Axum, pass a shared, arc-wrapped client to your routes to reuse a single configured client and reduce the chance of accidental insecure usage.

use aws_sdk_dynamodb::Client;
use std::sync::Arc;
use axum::routing::get;
use axum::Router;

async fn health_check(client: Arc<Client>) -> String {
    // Perform a lightweight operation, e.g., list tables, to validate connectivity
    match client.list_tables().send().await {
        Ok(_) => "ok".to_string(),
        Err(e) => format!("error: {:?}", e),
    }
}

#[tokio::main]
async fn main() {
    let client = Arc::new(build_dynamodb_client().await);
    let app = Router::new()
        .route("/health", get(move || health_check(Arc::clone(&client))));
    axum::Server::bind(&("0.0.0.0:3000".parse().unwrap()))
        .serve(app.into_make_service())
        .await
        .unwrap();
}

Example: Validate and sanitize all inputs that map to DynamoDB key conditions or expression attribute values to prevent injection-like manipulations. Use strongly-typed structures and avoid concatenating raw strings into expression attribute values.

use aws_sdk_dynamodb::types::AttributeValue;

fn make_expression(name: &str) -> String {
    // Ensure the name is a valid attribute name; do not interpolate user values directly
    format!("#status = :val")
}

fn make_values(status: &str) -> std::collections::HashMap<String, AttributeValue> {
    let mut values = std::collections::HashMap::new();
    values.insert(":val".to_string(), AttributeValue::S(status.to_string()));
    values
}

Example: Avoid logging raw responses or requests that may contain credentials or sensitive payloads. If logging is required, redact AWS signature components and PII.

// Do not log full responses; if necessary, mask sensitive fields
fn safe_log_table_name(table_name: &str) {
    // Only log business identifiers, not request IDs or tokens
    tracing::info!(table = %table_name, "listing tables");
}