Command Injection in Axum with Dynamodb

Command Injection occurs when an attacker can influence command-line arguments or shell commands constructed by an application. In an Axum application that interacts with DynamoDB, the risk typically arises not from DynamoDB itself, which is a managed NoSQL service, but from how application code builds shell commands to interact with AWS resources or other system utilities. For example, if an Axum handler receives user input such as a DynamoDB table name, partition key value, or a tag key and passes it directly to a command executed via std::process::Command or a shell utility, the input can be used to inject additional shell commands.

Consider an endpoint that accepts a table_name parameter and uses it to run aws dynamodb describe-table. If the input is not strictly validated or sanitized, an attacker could provide a value like mytable; cat /etc/passwd, leading to unintended command execution. Even when using the AWS SDK for Rust, constructing query parameters from uncontrolled input can lead to unsafe interactions downstream, such as logging or error messages that are later processed by external tooling.

The combination of Axum, a Rust web framework, and DynamoDB is common in serverless or cloud-native backends. While the AWS SDK for Rust prevents direct injection into API requests, developers may inadvertently introduce command injection through auxiliary tooling, scripts, or diagnostic commands that incorporate user-controlled data. The vulnerability is not inherent to Axum or DynamoDB but emerges from unsafe handling of input when constructing system-level commands.

Real-world attack patterns mirror those seen in OWASP API Top 10 A03:2023 — Injection, where untrusted data is sent to an interpreter as part of a command or query. In this context, DynamoDB table or attribute names become vectors for injection if used to build shell commands. For instance, a log rotation script triggered by a table name could execute aws dynamodb list-tables | grep {table_name} without proper escaping, enabling command chaining via ; or |.

To detect such issues, scanners like middleBrick perform black-box testing against the unauthenticated attack surface of the API. They do not rely on internal architecture but instead send crafted payloads that would trigger anomalous behavior if command injection is present. Findings include evidence of unsafe command construction, often tied to missing input validation or insufficient output sanitization.

Remediation focuses on strict input validation, avoiding shell usage, and using SDK methods that treat input as data, not executable instructions.

1. Avoid Shell Commands Entirely

Use the AWS SDK for Rust (aws-sdk-dynamodb) directly without invoking external processes. This eliminates the injection vector.

use aws_sdk_dynamodb::Client;
use axum::{routing::get, Router};

async fn describe_table_handler(
    axum::extract::Query(params): axum::extract::Query<HashMap<String, String>>
) -> Result<String, (axum::http::StatusCode, String)> {
    let config = aws_config::load_from_env().await;
    let client = Client::new(&config);
    // Assume table_name is validated against a strict allowlist
    let table_name = params.get("table_name").ok_or((axum::http::StatusCode::BAD_REQUEST, "missing table_name".to_string()))?;
    
    // Validate table_name format: only alphanumeric and hyphens
    if !table_name.chars().all(|c| c.is_alphanumeric() || c == '-' || c == '_') {
        return Err((axum::http::StatusCode::BAD_REQUEST, "invalid table name".to_string()));
    }

    let resp = client.describe_table().table_name(table_name).send().await;
    match resp {
        Ok(output) => Ok(format!("{:#?}", output)),
        Err(e) => Err((axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string())),
    }
}

#[tokio::main]
async fn main() {
    let app = Router::new().route("/table", get(describe_table_handler));
    axum::Server::bind(&"0.0.0.0:3000".parse().unwrap())
        .serve(app.into_make_service())
        .await
        .unwrap();
}

2. Strict Allowlisting for DynamoDB Identifiers

Table and index names in DynamoDB follow specific patterns. Validate input against these patterns rather than trying to sanitize dangerous characters.

fn is_valid_dynamodb_name(name: &str) -> bool {
    // DynamoDB names: 3-255 characters, letters, numbers, underscore, hyphen, period
    let re = regex::Regex::new(r"^[a-zA-Z0-9_.-]{3,255}$").unwrap();
    re.is_match(name)
}

async fn get_item_handler(
    axum::extract::Query(params): axum::extract::Query<HashMap<String, String>>
) -> Result<String, (axum::http::StatusCode, String)> {
    let table_name = params.get("table").ok_or((axum::http::StatusCode::BAD_REQUEST, "missing table".to_string()))?;
    let key = params.get("key").ok_or((axum::http::StatusCode::BAD_REQUEST, "missing key".to_string()))?;

    if !is_valid_dynamodb_name(table_name) || !is_valid_dynamodb_name(key) {
        return Err((axum::http::StatusCode::BAD_REQUEST, "invalid identifier".to_string()));
    }

    let config = aws_config::load_from_env().await;
    let client = Client::new(&config);
    let resp = client.get_item().table_name(table_name).key("id", aws_sdk_dynamodb::types::AttributeValue::S(key.clone())).send().await;
    // handle response
    Ok(format!("{:#?}", resp))
}

3. Secure Logging and Error Handling

Ensure that user input is not reflected into logs or error messages in a way that could be used for injection. Avoid passing raw input to shell-based log rotation or debugging commands.

use tracing::info;

async fn safe_logging_example(table_name: &str) {
    // Good: log sanitized or validated identifiers
    if is_valid_dynamodb_name(table_name) {
        info!(table_name, "Describing table");
    } else {
        tracing::warn!(?table_name, "invalid table name in request");
    }
}

By relying on the AWS SDK and strict input validation, Axum applications can safely interact with DynamoDB without exposing command injection risks. middleBrick scans can verify that no shell commands are constructed with user-controlled data and that API endpoints follow secure coding practices.