Cryptographic Failures in Axum with Dynamodb

When building an API in Axum that persists data to DynamoDB, cryptographic failures typically arise from how data is handled before it reaches the database and how keys are managed. Axum does not enforce encryption at the application layer; it is the developer’s responsibility to ensure sensitive fields are encrypted before serialization and that DynamoDB is not inadvertently exposed to unencrypted data paths.

One common pattern is to place sensitive values—such as personal identifiers, authentication tokens, or payment metadata—into a DynamoDB item without encryption. Because DynamoDB stores data at rest using AWS-owned keys, developers may assume this is sufficient. middleBrick detects this as Data Exposure when unencrypted sensitive fields are observed in database operations that should be encrypted. This becomes critical when items are retrieved and logged or transmitted to downstream services without re-encryption, exposing secrets in memory or logs.

Axum routes and extractors can inadvertently pass plaintext secrets into responses or into tracing contexts if middleware does not filter sensitive payloads. middleBrick’s Property Authorization checks flag cases where sensitive properties are read or written without explicit authorization checks. In addition, if the application uses an OpenAPI spec that describes these endpoints, middleBrick cross-references the spec with runtime behavior to ensure declared encryption expectations align with actual data flows.

LLM-related risks can also emerge if an Axum service exposes an endpoint that returns model outputs containing DynamoDB keys or PII. middleBrick’s LLM/AI Security checks look for system prompt leakage patterns and scan model responses for API keys or executable code. Even if the LLM integration is indirect—such as an admin tool that queries DynamoDB and feeds results into an LLM—unauthenticated endpoints or missing output validation can lead to prompt injection or data exfiltration.

Real-world attack patterns include insecure direct object references (BOLA/IDOR) where an attacker iterates over identifiers to access encrypted records, or insufficient input validation that allows injection of malicious payloads targeting DynamoDB condition expressions. middleBrick runs parallel checks for BOLA/IDOR and Input Validation to surface these issues alongside encryption gaps.

Remediation centers on encrypting sensitive fields before serialization, using envelope encryption where appropriate, and ensuring DynamoDB operations never handle plaintext secrets. Below are concrete Axum examples that integrate encryption before writing to DynamoDB and validate inputs to prevent injection.

Use AES-GCM to encrypt sensitive fields before constructing DynamoDB items. Keep keys in environment-managed secrets and never log raw values.

use axum::{routing::post, Router};
use aws_sdk_dynamodb::Client;
use serde::{Deserialize, Serialize};
use std::net::SocketAddr;
use aes_gcm::{Aes256Gcm, Key, Nonce, aead::{Aead, OsRng, generic_array::GenericArray}};

#[derive(Serialize, Deserialize)]
struct UserRecord {
    user_id: String,
    email_encrypted: String,
    ssn_encrypted: String,
}

async fn create_user(
    client: Client,
    body: UserRecord,
) -> Result<(), (axum::http::StatusCode, String)> {
    // Keys should be sourced securely, e.g., AWS KMS or env vars
    let key_bytes = hex::decode(std::env::var("ENC_KEY_HEX").map_err(|_| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, "key error"))?)?;
    let key = Key::::from_slice(&key_bytes);
    let cipher = Aes256Gcm::new(key);
    let nonce = Nonce::from_slice(b"unique nonce 12"); // derive per-record in production

    let email_encrypted = cipher.encrypt(nonce, body.email.as_bytes())
        .map_err(|_| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, "encryption failed"))?;
    let ssn_encrypted = cipher.encrypt(nonce, body.ssn.as_bytes())
        .map_err(|_| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, "encryption failed"))?;

    let item = aws_sdk_dynamodb::types::PutItemInput::builder()
        .table_name("users")
        .insert_item("user_id", aws_sdk_dynamodb::types::AttributeValue::S(body.user_id))
        .insert_item("email", aws_sdk_dynamodb::types::AttributeValue::B(email_encrypted.into()))
        .insert_item("ssn", aws_sdk_dynamodb::types::AttributeValue::B(ssn_encrypted.into()))
        .build()
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    client.put_item().set_input(Some(item)).send().await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;
    Ok(())
}

#[tokio::main]
async fn main() {
    let config = aws_config::load_from_env().await;
    let client = Client::new(&config);
    let app = Router::new().route("/users", post(create_user));
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}

Validate input to avoid injection and ensure fields conform to expected formats before encryption.

use axum::extract::Query;
use serde::Deserialize;
use validator::Validate;

#[derive(Deserialize, Validate)]
struct UserQuery {
    #[validate(length(min = 1))]
    filter_email: String,
}

async fn search_users(
    Query(params): Query,
) -> Result {
    params.validate().map_err(|e| (axum::http::StatusCode::BAD_REQUEST, e.to_string()))?;
    // Proceed with sanitized params
    Ok(())
}

middleBrick’s scans will highlight Data Exposure when plaintext sensitive fields are observed and will map findings to OWASP API Top 10 and compliance frameworks. Its LLM/AI Security checks can identify endpoints that may leak DynamoDB metadata or keys in model outputs, prompting developers to add output scanning and authorization guards.