Insecure Direct Object Reference in Actix with Dynamodb

Insecure Direct Object Reference (IDOR) in an Actix web service that uses DynamoDB occurs when an endpoint identifies a resource solely by a user-controlled identifier such as a path or query parameter without verifying that the authenticated caller is authorized to access that specific item. For example, an endpoint like /users/{user_id}/profile may use the user_id to fetch a DynamoDB item via a key condition like user_id = :uid. If the service skips an authorization check that ties the authenticated principal to the requested user_id, an attacker can change user_id to another valid identifier and access or modify data that belongs to other users.

DynamoDB itself does not enforce application-level permissions; it only enforces the identity of the caller via the credentials used for API calls. In Actix, if the application uses those credentials broadly (for example, a shared service account or IAM role assigned to the instance) or relies only on the presence of a record without validating ownership, the vulnerability is exposed. An attacker may leverage this to perform BOLA (Broken Object Level Authorization) attacks, enumerating valid IDs through timing differences or error messages, or combine IDOR with BFLA (Business Logic Abuse) to escalate privileges by changing role fields in the retrieved item.

Consider an endpoint that retrieves an order by order_id and returns item details without confirming the order belongs to the requesting customer. The DynamoDB query might use a composite key where order_id is the partition/sort key, but if the Actix handler does not also verify that the authenticated user’s ID matches the customer_id attribute in the item, the endpoint is vulnerable. Because DynamoDB queries return the item directly when keys match, the absence of a server-side authorization boundary allows IDOR.

OpenAPI specifications can unintentionally document these risks if path parameters are described as required without clarifying authorization requirements. During scanning, middleBrick cross-references the spec definitions with runtime behavior to highlight where object references are exposed without corresponding access controls.

Remediation centers on enforcing ownership or role-based checks before performing DynamoDB operations and designing keys to minimize exposure. In Actix, this means validating that the authenticated subject has permission to access the specific item, typically by including the subject identifier in the key expression or adding explicit authorization logic.

1. Embed the subject in the key design

Structure your DynamoDB key so that queries require the subject identifier as part of the key. This ensures that even if an attacker manipulates the identifier, they cannot access items outside their partition. For example, prefix the partition key with the user ID:

// Good: partition key includes user_id
const user_id = "user-123";
const order_id = req.match_info().get("order_id").unwrap();
let key = HashMap::from([
    ("pk", format!("USER#{}", user_id).as_str().into()),
    ("sk", format!("ORDER#{}", order_id).as_str().into()),
]);
let input = QueryInput {
    table_name: "Orders".into(),
    key_condition_expression: Some("pk = :pk AND begins_with(sk, :sk)".into()),
    expression_attribute_values: Some(HashMap::from([
        (":pk", AttributeValue::S("USER#user-123".into())),
        (":sk", AttributeValue::S("ORDER#order-456".into())),
    ])),
    ..Default::default()
};

2. Enforce ownership in the handler

If key design cannot be changed, add an explicit check after retrieving the item. Compare the authenticated user ID with the item’s owner attribute before returning data:

// Actix handler with authorization check
async fn get_order(
    req: HttpRequest,
    body: web::Data,
) -> Result<HttpResponse, Error> {
    let db_client = &body.db_client;
    let principal_id = req.extensions().get::().unwrap(); // authenticated user ID
    let order_id = req.match_info().get("order_id").unwrap();

    let output = db_client.get_item().await.map_err(|e| ...)?;
    let item = output.item.ok_or(...)?;

    // Ensure the item belongs to the requesting user
    if item.get("user_id").and_then(|v| v.as_s()) != Some(&principal_id) {
        return Err(error::ErrorForbidden("Unauthorized"));
    }

    Ok(HttpResponse::Ok().json(item))
}

3. Use condition expressions to prevent unauthorized updates

When modifying items, include a condition that the subject matches the owner. This prevents tampering even if the attacker guesses or iterates IDs:

let update = UpdateItemInput {
    table_name: "Orders".into(),
    key: HashMap::from([("pk", AttributeValue::S("ORDER#order-456".into())),
                        ("sk", AttributeValue::S("metadata".into()))]),
    update_expression: Some("set #st = :st".into()),
    condition_expression: Some("user_id = :uid".into()),
    expression_attribute_names: Some(HashMap::from([("#st", "status".into())])),
    expression_attribute_values: Some(HashMap::from([
        (":st", AttributeValue::S("shipped".into())),
        (":uid", AttributeValue::S("user-123".into())),
    ])),
    ..Default::default()
};
db_client.update_item().send().await.map_err(...)?;

4. Apply least-privilege IAM for the Actix service role

Configure the runtime credentials (if applicable) with policies that restrict actions to specific keys or attributes. Combine with DynamoDB fine-grained access control where supported to limit the scope of what the service can read or write.

middleBrick’s scans detect IDOR patterns across authentication and property authorization checks. By cross-walking spec definitions with observed behavior, it surfaces missing ownership validation and excessive permissions in DynamoDB access patterns.