Sql Injection in Axum with Dynamodb

SQL Injection is commonly associated with relational databases, but similar injection risks can manifest when query parameters are improperly concatenated into request paths, query strings, or conditional logic before being passed to a database client. In the Axum ecosystem, if user-controlled input is used to construct DynamoDB API parameters such as KeyConditionExpression, FilterExpression, or ExpressionAttributeNames, injection-like behavior can occur via unexpected expression syntax. For example, an attacker may attempt to inject expressions through path parameters to influence which attributes are queried or to force evaluation of reserved words.

Consider an Axum handler that builds a DynamoDB query based on user input without strict validation or parameterization:

// WARNING: illustrative example of unsafe concatenation
let user_input = query_params.get("user_id");
let key_expr = format!("id = :uid");
let expr_attr = hashmap!{":uid".to_string() => AttributeValue::S(user_input.unwrap().to_string())};
let req = QueryRequest {
    table_name: "Users".to_string(),
    key_condition_expression: Some(key_expr),
    expression_attribute_names: None,
    expression_attribute_values: Some(expr_attr),
    ..Default::default()
};

If the framework or developer does not strictly validate the structure of the expression itself and directly interpolates user input into the expression string, the input may alter the semantics of the request in unintended ways. While DynamoDB does not support traditional SQL syntax, its expression syntax can be abused to bypass intended filtering, cause unexpected condition evaluation, or probe schema details through error differences. This maps to common API security findings such as BOLA/IDOR and Improper Input Validation within middleBrick’s 12 checks.

middleBrick detects such patterns during unauthenticated black-box scanning by analyzing the API surface, including OpenAPI/Swagger specifications and runtime behavior. It flags insecure usage of expression parameters and highlights risks aligned with OWASP API Top 10 categories. Developers should treat all user-controlled data as untrusted and avoid building expression strings via concatenation, even when using a NoSQL service like DynamoDB.

Remediation centers on strict separation of data and expression structure. Use DynamoDB’s provided mechanisms for attribute names and values, and avoid any direct string interpolation of user input into expression fields. In Axum, implement typed extractors and validation layers before constructing requests.

1. Use expression attribute names for dynamic field names and expression attribute values for all data inputs:

use aws_sdk_dynamodb::types::AttributeValue;
use axum::extract::Query;
use serde::Deserialize;

#[derive(Deserialize)]
struct QueryParams {
    user_id: String,
}

async fn get_user_handler(
    Query(params): Query<QueryParams>,
    client: &aws_sdk_dynamodb::Client,
) -> Result<impl IntoResponse, (StatusCode, String)> {
    let req = QueryRequest {
        table_name: "Users".to_string(),
        key_condition_expression: Some("#id = :uid".to_string()),
        expression_attribute_names: Some({
            let mut map = HashMap::new();
            map.insert("#id".to_string(), "id".to_string());
            map
        }),
        expression_attribute_values: Some({
            let mut map = HashMap::new();
            map.insert(":uid".to_string(), AttributeValue::S(params.user_id));
            map
        }),
        ..Default::default()
    };
    let result = client.query().send().await;
    // handle result
    Ok(Json(result))
}

2. Validate and constrain input values strictly. For identifiers, enforce format rules (e.g., UUID or numeric patterns) before using them in requests:

use validator::Validate;

#[derive(Deserialize, Validate)]
struct QueryParams {
    #[validate(length(min = 1, max = 36), regex = "^\\\\p{Xid}*$")]
    user_id: String,
}

async fn validated_handler(
    Query(params): Query<Validated<QueryParams>>,
    client: &aws_sdk_dynamodb::Client,
) -> Result<impl IntoResponse, (StatusCode, String)> {
    // Safe to use params.user_id in expression attribute values
}

3. Prefer condition builders or SDK constructs that avoid raw expression strings where possible, or use middleware that enforces schema-aware parameterization. middleBrick’s CLI can scan your endpoints to highlight risky patterns in expression handling, and the Pro plan enables continuous monitoring to catch regressions early.

By consistently using expression attribute names/values and validating inputs, you align with secure-by-design practices. This approach reduces the attack surface for injection-style issues and supports compliance mappings to frameworks such as OWASP API Top 10 and SOC2, which middleBrick reports can reference directly.