Use After Free in Axum with Cockroachdb

Use After Free occurs when an application continues to use a pointer after the associated memory has been deallocated. In the context of an Axum API that interacts with CockroachDB, this typically arises when a request-scoped object (such as a connection pool client or a deserialized query result) is freed while an asynchronous operation still holds a reference to it.

Consider an Axum handler that obtains a CockroachDB client from a pool, executes an async query, and then drops the client prematurely due to a logic error or incorrect ownership handling. If the handler spawns a task that outlives the client’s lifetime, the background task may attempt to use the client to send further requests. Because Rust’s async runtime may schedule that task after the client has been deallocated, this results in Use After Free behavior, which can lead to memory corruption or information disclosure.

With CockroachDB, the risk is compounded by connection pooling and retries. For example, if an Axum handler does not properly scope the lifetime of a cockroachdb-rs client or a row object across .await points, the underlying memory can be reused for other allocations. An attacker may exploit this by inducing high concurrency or malformed requests that trigger aggressive dropping or re-use of connections and buffers, potentially leaking sensitive data from freed memory.

Real-world triggers include:

• Sharing non-Arc-wrapped clients across threads without ensuring proper lifetimes.
• Using tokio::spawn without explicitly moving owned data into the spawned task, causing references to outlive their referent.
• Relying on frameworks or ORMs that cache or reuse query result buffers without correctly resetting or re-allocating them between requests.

Because middleBrick tests the unauthenticated attack surface and includes checks for unsafe consumption patterns and input validation, it can surface indicators that an API endpoint may expose memory safety issues when handling database interactions, even though the scanner does not fix the root cause.

To prevent Use After Free in Axum when using CockroachDB, ensure that all data used across .await points is owned and properly reference-counted. The following practices and code examples illustrate secure patterns.

1. Use Arc to share the CockroachDB client safely

Wrap your database client in an Arc (atomic reference count) so that cloned handles can safely outlive the scope of the request. This ensures the underlying connection remains valid for the duration of any asynchronous work.

use std::sync::Arc;
use cockroachdb_rs::Client;

struct AppState {
    db: Arc<Client>,
}

async fn handler(
    State(state): State<Arc<AppState>>,
) -> Result<impl IntoResponse, (StatusCode, String)> {
    let client = Arc::clone(&state.db);
    let result = client.query("SELECT id, name FROM users WHERE status = $1", &[&"active"]).await?;
    // process rows...
    Ok(Json(result))
}

2. Move owned data into spawned tasks

When spawning asynchronous tasks, move the client and any necessary data into the task to avoid holding references beyond their lifetime.

use tokio::task;

async fn handle_request(db: Arc<Client>, user_id: i64) {
    task::spawn(async move {
        // db is moved into the task and lives as long as the task runs
        let _ = db.query("SELECT * FROM audit_log WHERE user_id = $1", &[&user_id]).await;
    });
}

3. Avoid returning references to temporary data

Ensure that any data extracted from CockroachDB rows is owned (e.g., String, Vec<u8>) rather than borrowed, particularly when caching or storing results.

async fn fetch_user_name(db: &Client, id: i64) -> Result<String, db_error> {
    let row = db.query_one("SELECT name FROM users WHERE id = $1", &[&id]).await?;
    let name: String = row.get(0); // owned copy
    Ok(name)
}

4. Use structured query results and serialization

Map rows to owned structs and serialize/deserialize explicitly to avoid holding onto raw buffers that may be reused or freed incorrectly.

use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
struct User {
    id: i64,
    name: String,
}

async fn user_to_struct(db: &Client, id: i64) -> Result<User, db_error> {
    let row = db.query_one("SELECT id, name FROM users WHERE id = $1", &[&id]).await?;
    let user = User {
        id: row.get(0),
        name: row.get(1),
    };
    Ok(user)
}

5. Leverage Axum extractors with proper lifetimes

When passing state into handlers, prefer State<T> where T is Send + Sync + 'static, ensuring that the framework does not inadvertently keep references to transient data.

async fn secure_handler(
    State(config): State<Arc<AppConfig>>,
    Extension(db): Extension<Arc<Client>>,
) -> impl IntoResponse {
    // Both config and db are safely shared and owned
    (StatusCode::OK, format!("Connected to cluster: {}", config.cluster_name))
}

By combining these patterns, you eliminate the conditions that lead to Use After Free when Axum routes interact with CockroachDB. middleBrick’s checks for unsafe consumption and input validation can help identify endpoints that may rely on unsafe patterns, supporting a more secure deployment posture.