Broken Access Control in Axum with Dynamodb

Broken Access Control (BAC) in an Axum service backed by DynamoDB typically occurs when authorization checks are missing, inconsistent, or bypassed at the API boundary and the data layer. In this stack, the vulnerability arises because authorization logic is either not applied before constructing DynamoDB requests or is applied at a coarse granularity, allowing horizontal or vertical privilege escalation. For example, an endpoint like /users/{user_id}/profile might accept a path parameter user_id but fail to verify that the authenticated subject is allowed to access that specific item. Because DynamoDB queries are constructed dynamically using that parameter, an attacker can change the ID to access another user’s data, demonstrating a classic Insecure Direct Object Reference (IDOR) that maps to the BOLA/IDOR check in middleBrick’s 12 security scans.

In Axum, route extraction and handler logic are close to the wire, which can lead to subtle authorization gaps when developers rely on middleware alone. Middleware may enforce authentication (e.g., validating a JWT) but not enforce fine-grained ownership or role checks before issuing DynamoDB GetItem or Query requests. If the DynamoDB table uses a composite key design (partition key as PK such as USER#123 and sort key as SK such as PROFILE), missing validation of the partition key against the subject’s identity permits horizontal privilege escalation across users sharing the same table. Vertical privilege escalation can occur when an endpoint intended for regular users inadvertently allows administrative operations because role claims in the token are not validated before issuing UpdateItem or DeleteItem requests.

Additionally, over-permissive IAM policies attached to the service’s execution role can amplify BAC in the DynamoDB interaction. If the role allows dynamodb:Scan or broad dynamodb:GetItem on the table, a compromised or misconfigured handler could expose more data than intended. The interplay between Axum’s routing flexibility and DynamoDB’s key-based access model means developers must explicitly encode authorization in each handler and ensure the request context (subject ID, roles, scopes) is validated against the key condition expressions or filter logic before execution. Without this, the API surface remains vulnerable to unauthenticated or low-privilege access paths that middleBrick’s BOLA/IDOR and Authentication checks are designed to surface.

To remediate Broken Access Control in Axum with DynamoDB, enforce subject-to-item mapping at the handler level and validate authorization before constructing any request to DynamoDB. Use typed models and ensure that every data access includes the subject identifier derived from the authentication context. Below are concrete, working Axum handler examples that demonstrate secure patterns using the AWS SDK for Rust.

Secure handler with partition key binding

Ensure the handler derives the expected partition key from the authenticated subject and rejects requests where the provided ID does not match. This prevents IDOR across user boundaries.

use axum::{routing::get, Router, extract::State};
use aws_sdk_dynamodb::Client;
use serde::{Deserialize, Serialize};
use std::sync::Arc;

#[derive(Clone)]
struct AppState {
    dynamodb: Client,
    table_name: String,
}

#[derive(Debug, Deserialize)]
struct ProfilePath {
    user_id: String,
}

#[derive(Serialize, Deserialize)]
struct Profile {
    user_id: String,
    display_name: String,
}

async fn get_profile(
    State(state): State>,
    auth: Option, // your auth extractor providing subject
    Path(params): Path,
) -> Result<impl IntoResponse, (axum::http::StatusCode, String)> {
    let subject = auth.ok_or((axum::http::StatusCode::UNAUTHORIZED, "missing auth"))?;
    // Ensure the requested user_id matches the authenticated subject
    if subject.user_id != params.user_id {
        return Err((axum::http::StatusCode::FORBIDDEN, "access denied".to_string()));
    }
    let pk = format!("USER#{}", params.user_id);
    let resp = state.dynamodb
        .get_item()
        .table_name(&state.table_name)
        .key("PK", aws_sdk_dynamodb::types::AttributeValue::S(pk))
        .key("SK", aws_sdk_dynamodb::types::AttributeValue::S("PROFILE".to_string()))
        .send()
        .await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    let item = resp.item().ok_or((axum::http::StatusCode::NOT_FOUND, "not found"))?;
    let profile = Profile {
        user_id: item.get("user_id").and_then(|v| v.as_s().ok()).unwrap_or(&"".to_string()).clone(),
        display_name: item.get("display_name").and_then(|v| v.as_s().ok()).unwrap_or(&"".to_string()).clone(),
    };
    Ok(axum::Json(profile))
}

fn main() {
    let config = aws_config::load_from_env().await;
    let client = Client::new(&config);
    let app_state = Arc::new(AppState {
        dynamodb: client,
        table_name: "app_table".to_string(),
    });
    let app = Router::new()
        .route("/users/:user_id/profile", get(get_profile))
        .with_state(app_state);
    // axum::Server::bind(&("0.0.0.0:3000".parse().unwrap())).serve(app.into_make_service()).await.unwrap();
}

Secure query with explicit key condition and role checks

For operations that query related data, bind the partition key to the subject and apply role-based filters before invoking DynamoDB. This aligns with the Principle of Least Privilege at the handler level.

async fn list_user_posts(
    State(state): State>,
    auth: Option,
) -> Result<impl IntoResponse, (axum::http::StatusCode, String)> {
    let subject = auth.ok_or((axum::http::StatusCode::UNAUTHORIZED, "missing auth"))?;
    let pk = format!("USER#{}", subject.user_id);
    let resp = state.dynamodb
        .query()
        .table_name(&state.table_name)
        .key_condition_expression("PK = :pk")
        .expression_attribute_values(
            ":pk",
            aws_sdk_dynamodb::types::AttributeValue::S(pk),
        )
        .filter_expression("SK begins_with :sk_prefix")
        .expression_attribute_values(
            ":sk_prefix",
            aws_sdk_dynamodb::types::AttributeValue::S("POST".to_string()),
        )
        .send()
        .await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    let posts: Vec<_> = resp.items().unwrap_or_default()
        .iter()
        .filter_map(|item| {
            Some(Post {
                id: item.get("id")?.as_s().ok()?.clone(),
                content: item.get("content")?.as_s().ok()?.clone(),
            })
        })
        .collect();
    Ok(axum::Json(posts))
}

These examples illustrate that the authorization boundary must be enforced in Axum before any DynamoDB call, using the subject identity to constrain keys (partition key binding) and avoiding generic or unscoped queries. This directly addresses the BOLA/IDOR and Authentication checks performed by middleBrick, reducing the risk of data exposure mapped to OWASP API Top 10 and relevant compliance frameworks.