Api Key Exposure in Axum with Mysql

When building an Axum service that connects to a Mysql backend, developers often embed database credentials or API keys in application configuration or source code. If these values are accidentally exposed through logs, error messages, or insecure deserialization, an attacker can harvest them and pivot to your Mysql instance.

Axum does not inherently leak secrets, but common patterns increase risk:

• Database connection strings built from environment variables that are logged during startup or panic handling.
• Structured error responses that include full database errors, revealing table or column names and exposing whether Mysql returns stack traces in certain configurations.
• HTTP handler code that passes user input directly into Mysql queries without validation, enabling information disclosure through timing differences or error-based techniques.

middleBrick detects API key exposure by analyzing the unauthenticated attack surface of your Axum endpoints. It flags endpoints that return server headers, verbose error payloads, or responses containing patterns resembling database credentials or API keys. When combined with Mysql, findings often include:

• SQL injection vectors that allow extraction of Mysql user credentials stored in a users table.
• Missing rate limiting on authentication endpoints, enabling credential stuffing against the Mysql-backed identity store.
• Insecure deserialization in Axum state or session handlers that may expose serialized Mysql connection parameters.

During a scan, middleBrick runs active prompt injection tests and system prompt leakage checks tailored for AI endpoints, but for traditional Axum+Mysql services it focuses on input validation, authentication, and data exposure categories. The scanner cross-references findings with the OpenAPI spec if provided, ensuring that paths expecting authentication tokens are not inadvertently exposing Mysql-related data in responses.

Remediation guidance from middleBrick emphasizes least-privilege database users, strict input validation, and secure error handling. By rotating exposed keys and tightening Axum route guards, you reduce the chance of lateral movement from a compromised API layer into your Mysql storage layer.

Secure Axum applications interacting with Mysql by applying strict input validation, using parameterized queries, and ensuring secrets are managed outside the codebase. Below are concrete, working examples.

1. Secure database connection setup

Store Mysql credentials in environment variables and load them securely in Axum without logging them.

use axum::Router;
use sqlx::mysql::MySqlPoolOptions;
use std::env;

#[tokio::main]
async fn main() {
    // Load from environment without printing
    let database_url = env::var("MYSQL_URL").expect("MYSQL_URL must be set");
    let pool = MySqlPoolOptions::new()
        .max_connections(5)
        .connect(&database_url)
        .await
        .expect("Failed to create pool");

    let app = Router::new()
        .with_state(pool);
    // ... routes
}

2. Parameterized queries to prevent injection and exposure

Always use placeholders to avoid concatenating user input into SQL strings.

use axum::extract::State;
use sqlx::FromRow;
use serde::Serialize;

#[derive(FromRow, Serialize)]
struct User {
    id: i32,
    username: String,
}

async fn get_user(
    State(pool): State,
    user_id: String,
) -> Result, (axum::http::StatusCode, String)> {
    // Safe: parameterized query
    let user = sqlx::query_as::<_, User>("SELECT id, username FROM users WHERE id = ?")
        .bind(user_id.parse::().map_err(|_| (axum::http::StatusCode::BAD_REQUEST, "Invalid ID"))?)
        .fetch_one(&pool)
        .await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;
    Ok(axum::response::Json(user))
}

3. Error handling that avoids leaking Mysql details

Do not return raw database errors to the client; map them to generic messages while logging securely.

use axum::http::StatusCode;
use thiserror::Error;

#[derive(Error, Debug)]
pub enum ApiError {
    #[error("Request failed")]
    RequestFailed,
    #[error("Database error")]
    DatabaseError,
}

impl Into<(StatusCode, String)> for ApiError {
    fn into(self) -> (StatusCode, String) {
        match self {
            ApiError::RequestFailed => (StatusCode::BAD_REQUEST, self.to_string()),
            ApiError::DatabaseError => (StatusCode::INTERNAL_SERVER_ERROR, self.to_string()),
        }
    }
}

// In handler
async fn safe_handler() -> Result {
    // ...
    Ok(())
}

4. Rotate keys and audit Mysql user privileges

Ensure Mysql accounts used by Axum have minimal privileges. For example, a read-only endpoint user should not have INSERT/UPDATE rights.

-- Example Mysql statements for least-privilege access
CREATE USER 'axum_reader'@'%' IDENTIFIED BY 'StrongPassword123';
GRANT SELECT ON mydb.users TO 'axum_reader'@'%';
FLUSH PRIVILEGES;