Use After Free in Actix with Dynamodb

Use After Free occurs when memory is deallocated but references to it are still used. In an Actix web service that interacts with DynamoDB via the AWS SDK for Rust, this can arise through asynchronous request handling and SDK response lifetimes. Actix actors and handlers often spawn futures that capture references to request data or SDK clients. If the handler or a spawned future retains a reference to a deserialized structure or client state that has been dropped or moved, and later attempts to read or write through that reference, the behavior becomes undefined and may expose sensitive data or cause crashes.

Specifically, when using the AWS SDK for Rust with DynamoDB, the SDK returns futures that may borrow request-scoped objects or configuration handles. If an Actix handler does not properly own or clone these objects and instead holds a reference across an .await point, the referenced object might be freed once the handler or an intermediate future completes. Subsequent use of that reference in a continuation or callback results in Use After Free. This is exacerbated when combining Actix’s actor model and message passing with SDK responses that involve shared state or cached clients, where lifetimes are not always explicit.

An example pattern that can lead to Use After Free is capturing a reference to a deserialized DynamoDB item inside an async block that is sent between actors or stored in a context without ensuring the referenced data lives long enough. Because Actix processes messages asynchronously, the original data may be dropped before the async block executes, leaving a dangling pointer when the block attempts to access captured fields.

Real-world exposure via a security lens: an attacker could influence timing or message ordering (e.g., through high concurrency or crafted requests) to increase the likelihood that a use-after-free path is reached, potentially leading to information disclosure or instability. Although the AWS SDK manages its own memory, the integration surface in Actix handlers and message structs requires careful ownership semantics to avoid introducing use-after-free risks in application-level code.

Because middleBrick scans unauthenticated attack surfaces and tests input validation and runtime behaviors, it can surface indicators that an API endpoint behaves inconsistently under load or malformed inputs — patterns that may correlate with memory safety issues when the backend is implemented with unsafe Rust practices. Findings will include severity, remediation guidance, and mappings to OWASP API Top 10 and other frameworks relevant to memory-safety-related anomalies.

To prevent Use After Free in Actix when working with DynamoDB, ensure all data used across async boundaries is owned rather than borrowed. Prefer cloning data or using Arc to share ownership safely. The following examples show correct patterns for integrating DynamoDB with Actix handlers.

Example 1: Cloning data before moving into an async block

use actix_web::{web, HttpResponse, Result};
use aws_sdk_dynamodb::Client;
use serde::Deserialize;

#[derive(Deserialize, Clone)] // Ensure the struct can be cloned
struct QueryInput {
    table_name: String,
    key: String,
}

async fn get_item_handler(
    client: web::Data,
    input: web::Json,
) -> Result<HttpResponse> {
    let input_clone = input.into_inner(); // Clone owned data
    let client = client.clone();           // SDK client is already clone

    actix_web::web::block(move || {
        // Use owned data inside the blocking thread
        let runtime = tokio::runtime::Runtime::new().unwrap();
        runtime.block_on(async {
            let table = client.table(&input_clone.table_name);
            let key_response = table
                .get_item()
                .set_key(Some(aws_sdk_dynamodb::types::AttributeValue::S(input_clone.key)))
                .send()
                .await;
            // Handle response without referencing input_clone beyond this point
            match key_response {
                Ok(output) => HttpResponse::Ok().body(format!(