Api Key Exposure in Axum with Dynamodb

When building a Rust API service with the Axum web framework that uses Amazon DynamoDB as a backend data store, developers often pass sensitive API credentials through request handling paths that are not properly isolated. Axum applications typically rely on shared state to provide database clients to route handlers, and if that state contains AWS credentials used to instantiate a DynamoDB client, those credentials can be inadvertently exposed through logging, error responses, or misconfigured CORS and middleware.

DynamoDB operations in Axum commonly use the AWS SDK for Rust (aws-sdk-dynamodb), where a client is constructed with an AWS credentials provider (e.g., aws_config::from_env().load().await). If the application bundles this client within request-scoped state or returns raw configuration objects in error paths, API keys or temporary session tokens may appear in stack traces, HTTP responses, or application logs. For example, a poorly structured handler that returns a dynamodb_client.describe_table() error directly to the client might include credential metadata in serialized error formats, especially when tracing or debugging middleware is active.

The risk is compounded when Axum routes expose administrative endpoints that reinitialize or reconfigure the DynamoDB client using credentials passed via environment variables or configuration files. If those endpoints are not properly protected with authentication and authorization checks, an unauthenticated attacker can trigger code paths that reveal sensitive information through verbose error messages or misconfigured OpenAPI documentation generated from route introspections. This aligns with the broader Authentication and Data Exposure checks performed by middleBrick, which flag endpoints that return sensitive context without requiring prior authentication.

Additionally, when Axum handlers construct AWS requests manually—for example, signing DynamoDB operations with inline credentials instead of using the SDK’s managed provider—developers may concatenate or log secret keys during request building. middleBrick’s LLM/AI Security checks specifically test for system prompt leakage and output scanning; if API keys appear in responses or logs due to improper error handling, these checks can detect the exposure pattern as a high-severity finding mapped to OWASP API Top 10 A01: Broken Object Level Authorization and A05: Security Misconfiguration.

Runtime scanning by middleBrick validates whether endpoints that interact with DynamoDB inadvertently disclose credentials through unchecked serialization or debug routes. The scanner tests unauthenticated attack surfaces and examines response payloads, headers, and server-side logs (where accessible) for patterns resembling AWS access keys, secret keys, or session tokens. This is critical because DynamoDB interactions often involve long-lived credentials if IAM roles are not correctly scoped, increasing the window of exposure for attackers.

To prevent API key exposure in an Axum application using DynamoDB, ensure that AWS credentials are never part of request state or response payloads. Use the AWS SDK for Rust’s default credential chain and configure the DynamoDB client at the application level without exposing secrets through route parameters or error responses.

Secure Axum State Management with DynamoDB

Define a shared application state that holds only the DynamoDB client, constructed outside of request handling using environment-managed credentials. This keeps sensitive material out of handler logic and prevents accidental serialization.

use aws_sdk_dynamodb::Client as DynamoDbClient;
use std::sync::Arc;
use axum::extract::State;

struct AppState {
    dynamodb_client: DynamoDbClient,
}

#[tokio::main]
async fn main() {
    let config = aws_config::load_from_env().await;
    let client = DynamoDbClient::new(&config);
    let app_state = Arc::new(AppState { dynamodb_client: client });

    let app = Router::new()
        .route("/items/:id", get(get_item))
        .with_state(app_state);

    axum::Server::bind(&"0.0.0.0:3000".parse().unwrap())
        .serve(app.into_make_service())
        .await
        .unwrap();
}

Safe DynamoDB Handler Implementation

Handlers should accept the client via state and avoid propagating errors that include raw configuration details. Use mapping to strip sensitive fields before returning errors to the client.

use aws_sdk_dynamodb::model::ResourceNotFoundException;
use axum::{response::IntoResponse, http::StatusCode};
use serde_json::json;

async fn get_item(
    State(state): State Result<impl IntoResponse, (StatusCode, String)> {
    let result = state.dynamodb_client
        .get_item()
        .table_name("Items")
        .key("id", aws_sdk_dynamodb::types::AttributeValue::S(id))
        .send()
        .await
        .map_err(|e| {
            // Avoid exposing internal error details
            (StatusCode::INTERNAL_SERVER_ERROR, "Request failed".to_string())
        })?;

    if let Some(item) = result.item {
        Ok(Json(item))
    } else {
        Err((StatusCode::NOT_FOUND, "Item not found".to_string()))
    }
}

IAM and Credential Scoping Best Practices

Ensure that the environment running the Axum service uses IAM roles with least-privilege permissions for DynamoDB. Do not embed access keys in source code or configuration files that may be loaded into route handlers. middleBrick’s BFLA/Privilege Escalation and Property Authorization checks validate whether endpoints enforce proper authorization and whether credentials are over-privileged for the operations they perform.

When using temporary credentials via AWS Security Token Service (STS), rotate keys frequently and avoid long-lived sessions. Configure the SDK to use instance profiles or IAM roles for ECS, EKS, or EC2 deployments rather than static keys. This reduces the risk of key leakage through logs or error outputs, which middleBrick’s Data Exposure scan specifically tests for by analyzing endpoint behavior under unauthenticated conditions.

Finally, integrate the middleBrick CLI into development workflows to scan endpoints regularly: middlebrick scan https://api.example.com. The tool checks for insecure credential handling patterns and maps findings to compliance frameworks such as PCI-DSS and SOC 2, helping teams catch DynamoDB-related misconfigurations before deployment.