Dangling Dns in Actix with Dynamodb

A dangling DNS configuration in an Actix-web service that interacts with DynamoDB can expose an unauthenticated attack surface during black-box scanning. When an Actix application resolves a hostname to a DynamoDB endpoint, if the DNS record becomes stale (for example, due to infrastructure changes, alias updates, or route changes) but the application still attempts to resolve and connect, the runtime may follow the dangling reference. During a scan, the tool can trigger requests that cause the Actix service to perform DNS lookups for the DynamoDB hostname. If the DNS response returns an unexpected or unintended IP, the application may route requests to a resource that is not properly isolated or access-controlled. This can lead to BOLA/IDOR-like conditions where one tenant or service namespace inadvertently interacts with another tenant’s DynamoDB data, or to SSRF-like outcomes where internal endpoints are reachable through the manipulated DNS resolution.

In the context of middleBrick’s 12 parallel checks, the scanner tests unauthenticated endpoints that rely on external resolution. For the DynamoDB integration in Actix, this means the scan can observe whether DNS-derived endpoints are validated before use. An example risk pattern: an Actix handler builds an AWS SDK client using a hostname stored in configuration or environment variables. If that hostname’s DNS record changes but the configuration is not updated, the handler may continue to resolve the name, potentially pointing to a misconfigured or public endpoint. The scanner does not inspect source code; it observes runtime behavior such as outbound connections to unexpected IPs, missing authorization on observed endpoints, or data exposure via returned payloads that should have been restricted to authenticated callers. These observations map to findings in categories such as Input Validation, BOLA/IDOR, Data Exposure, and SSRF.

Consider a concrete scenario: an Actix service uses the AWS SDK for Rust to get an item from a DynamoDB table, constructing the endpoint from a hostname variable. If the DNS entry for that hostname resolves to a different AWS account’s endpoint or an unintended proxy, the request may be authorized with incorrect credentials or none at all, depending on how the SDK picks up the region and signing context. The middleBrick scan can detect this by sending requests that cause the Actix service to initiate outbound DNS queries and connections, then checking whether responses contain sensitive data or whether authorization checks are bypassed. Findings may include missing property authorization, insecure input validation for user-supplied identifiers used to build table references, and risks consistent with OWASP API Top 10 and compliance frameworks such as SOC2 and GDPR.

To remediate dangling DNS risks in an Actix service that uses DynamoDB, validate and constrain endpoint resolution before constructing SDK clients. Prefer explicit AWS region and endpoint configuration over dynamic hostname resolution, and ensure that any user input used to reference tables or keys is strictly validated against an allowlist. The following examples show secure patterns using the official AWS SDK for Rust (aws-sdk-dynamodb) with Actix-web, including how to pass a static endpoint and enforce table-name validation.

Example 1: Using a static region and endpoint to avoid dangling DNS. By providing the region and an explicit HTTPS endpoint, you reduce reliance on runtime DNS that can become stale or redirect unexpectedly.

use aws_config::meta::region::RegionProviderChain;
use aws_sdk_dynamodb::Client;
use actix_web::{web, Responder};

async fn get_item_handler(
    client: web::Data,
    path: web::Path,
) -> impl Responder {
    let table_name = path.into_inner();
    // Validate table name against an allowlist to prevent IDOR/BOLA
    let allowed_tables = ["prod-users", "staging-config"];
    if !allowed_tables.contains(&table_name.as_str()) {
        return actix_web::HttpResponse::BadRequest().body("Invalid table");
    }
    let output = client
        .get_item()
        .table_name(&table_name)
        .key("id", aws_sdk_dynamodb::types::AttributeValue::S("user-123".into()))
        .send()
        .await;
    match output {
        Ok(resp) => actix_web::HttpResponse::Ok().body(format!("{:?}", resp)),
        Err(e) => actix_web::HttpResponse::InternalServerError().body(e.to_string()),
    }
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    let region_provider = RegionProviderChain::first_try(Some("us-east-1".parse().unwrap()));
    let config = aws_config::from_env().region(region_provider).load().await;
    let client = Client::new(&config);
    actix_web::HttpServer::new(move || {
        actix_web::App::new()
            .app_data(web::Data::new(client.clone()))
            .route("/items/{table_name}", actix_web::web::get().to(get_item_handler))
    })
    .bind("127.0.0.1:8080")?
    .run()
    .await
}

Example 2: Enforcing strict table-name and key patterns to mitigate IDOR/BOLA via input validation. This ensures that user-controlled identifiers cannot reference unexpected tables or keys that may lead to cross-tenant data exposure.

use aws_sdk_dynamodb::types::AttributeValue;
use actix_web::{post, web};

#[post("/users/{user_id}")]
async fn get_user(
    client: web::Data,
    path: web::Path<(String,)>, // user_id as path param
) -> Result {
    let (user_id,) = path.into_inner();
    // Validate user_id format to prevent IDOR
    if !user_id.chars().all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_') {
        return Err(actix_web::error::ErrorBadRequest("Invalid user_id"));
    }
    let output = client
        .get_item()
        .table_name("prod-users")
        .key(
            "user_id",
            AttributeValue::S(user_id),
        )
        .send()
        .await;
    match output {
        Ok(resp) => Ok(actix_web::HttpResponse::Ok().json(resp.into_inner().item)),
        Err(e) => Err(actix_web::error::ErrorInternalServerError(e.to_string())),
    }
}

These patterns emphasize explicit configuration and strict input validation, which align with how middleBrick’s checks for BOLA/IDOR, Input Validation, and Property Authorization can surface issues when DNS or configuration drift leads to unintended endpoints. By pinning endpoints and validating identifiers, you reduce the risk that a dangling DNS record can redirect traffic in a way that bypasses intended controls.