Ldap Injection in Axum with Dynamodb

Ldap Injection occurs when an attacker can manipulate LDAP query construction by injecting malicious input. In an Axum application that uses AWS SDK for Rust to interact with DynamoDB to store or retrieve user records used for LDAP authentication, improper handling of user-controlled input can lead to LDAP injection. For example, if Axum extracts a username or group filter from request parameters and directly concatenates it into an LDAP filter string before evaluating it against data fetched from DynamoDB, special characters such as (, ), *, or & can alter the filter logic. This can cause the LDAP query to return unintended entries or bypass authentication checks.

The DynamoDB aspect is indirect: DynamoDB itself does not interpret LDAP filters, but it may store user attributes (e.g., uid, memberOf, or distinguished names) that Axum uses to construct LDAP queries. If Axum builds LDAP filters by interpolating DynamoDB attribute values without escaping, the injection surface is introduced. A typical vulnerable pattern is building an LDAP filter like (&(uid=USER_INPUT)(objectClass=person)) where USER_INPUT comes from a DynamoDB attribute. An attacker supplying )(uid=admin as input could change the filter semantics, potentially returning all entries or authenticating as another user.

Because this scanning approach is black-box and tests the unauthenticated attack surface, Ldap Injection is identified when inputs that reach LDAP construction logic can modify filter structure. The 12 security checks include Authentication and Input Validation, which together flag cases where user-controlled data influences authentication filters without proper escaping.

To prevent Ldap Injection in an Axum service that references DynamoDB data, ensure that any user input used in LDAP filters is strictly validated and escaped. Avoid string concatenation for LDAP filters; instead, use an LDAP filter encoding library or implement strict allow-list validation for attributes that may originate from DynamoDB.

Below is a safe Rust example for Axum that retrieves a user record from DynamoDB and constructs an LDAP filter safely by avoiding direct interpolation of raw user input into the filter string. It uses parameterized comparisons and a simple allow-list check on the attribute intended for LDAP operations.

use axum::{routing::get, Router};
use aws_sdk_dynamodb::Client as DynamoClient;
use ldap3::LdapConnAsync;
use serde::Deserialize;

#[derive(Deserialize)]
struct UserRequest {
    username: String,
}

async fn handle_login(
    Form(payload): Form,
    dynamo_client: &DynamoClient,
) -> Result {
    // Validate input: allow only alphanumeric and a few safe characters
    if !payload.username.chars().all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '-') {
        return Err((axum::http::StatusCode::BAD_REQUEST, "Invalid username".into()));
    }

    // Fetch user metadata from DynamoDB (example)
    let item = dynamo_client
        .get_item()
        .table_name("users")
        .key("username", aws_sdk_dynamodb::types::AttributeValue::S(payload.username.clone()).into())
        .send()
        .await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    let dn = item.get("dn").and_then(|v| v.s.as_ref())
        .ok_or_else(|| (axum::http::StatusCode::UNAUTHORIZED, "User not found".into()))?;

    // Build LDAP filter safely: use parameterized filter components
    // Do NOT directly concatenate user input into the filter string
    let filter = format!("(&(objectClass=person)(uid={}))", ldap_escape::escape_filter_value(&payload.username));

    // Example LDAP bind using constructed filter and retrieved DN base
    let (conn, mut ldap) = LdapConnAsync::new("ldap://ldap.example.com").await.map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;
    let result = ldap.simple_bind(dn, "password_placeholder").await.map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    // Handle result...
    Ok("login flow completed".into())
}

#[tokio::main]
async fn main() {
    let config = aws_config::load_from_env().await;
    let dynamo_client = aws_sdk_dynamodb::Client::new(&config);
    let app = Router::new().route("/login", get(move |form| handle_login(form, &dynamo_client)));
    axum::Server::bind(&"0.0.0.0:3000".parse().unwrap())
        .serve(app.into_make_service())
        .await
        .unwrap();
}

Key remediation points:

• Input validation: restrict characters allowed in usernames to a safe subset.
• Do not build LDAP filters via string concatenation with raw DynamoDB-derived values.
• Use a dedicated escaping function (e.g., ldap_escape::escape_filter_value) on any user-controlled components that must appear in the filter.
• Treat DynamoDB-stored attributes as untrusted inputs when used in security-sensitive contexts like LDAP queries.