Ldap Injection in Axum with Mongodb

Ldap Injection occurs when user-controlled input is concatenated into an LDAP query without proper validation or escaping. In an Axum service that uses MongoDB as a backend data store, this typically manifests in application logic that first authenticates or queries an LDAP directory (for example to validate credentials or group membership) and then uses MongoDB to store or retrieve related identity data. The combination creates a two-stage attack surface: an attacker can abuse LDAP injection to bypass authentication or elevate privileges, and depending on how the application uses MongoDB, the same input may affect how identity data is stored or retrieved, increasing the blast radius.

Consider an endpoint that accepts a username and password, binds to an LDAP server to validate credentials, and then queries MongoDB for extended profile information. If the username is directly interpolated into the LDAP filter string, an attacker can supply input such as (uid=* to always match, potentially authenticating as any user. In Axum, this often occurs when building filters using format strings or when constructing the filter map without escaping special LDAP characters. Because Axum is asynchronous and strongly typed, developers might inadvertently trust deserialized request bodies and pass them straight into LDAP calls. MongoDB usage compounds the issue: if the application uses the same user-controlled input to build MongoDB queries (for example to fetch extended profile info), attackers may achieve NoSQL injection or unauthorized data access, especially if input is not validated before being used in MongoDB operations.

Real-world scenarios include endpoints that perform LDAP bind followed by a MongoDB find_one using the same username. If the username is not sanitized for LDAP special characters (such as *, (, ), &), the LDAP filter can be manipulated to return unintended matches. Additionally, if the application stores or indexes user input in MongoDB without normalization or strict schema enforcement, malicious LDAP payloads might be persisted and later used in queries, enabling injection across layers. The OWASP API Top 10 and related frameworks classify this as an authentication and injection risk, emphasizing the need to treat LDAP and database inputs as hostile even when they originate from internal systems.

middleBrick detects such issues by running active probes against the unauthenticated attack surface, including injection-style tests across authentication and data handling checks. It also cross-references OpenAPI specifications to identify endpoints that claim to handle identity-related operations and highlights findings that map to compliance frameworks such as OWASP API Top 10 and SOC2. Note that the scanner reports and provides remediation guidance but does not modify code or block execution.

To secure Axum services that integrate LDAP and MongoDB, treat all user input as untrusted and apply strict validation and parameterization at each boundary. For LDAP, use constant-time comparison where possible and avoid building filters via string concatenation. For MongoDB, prefer typed, schema-validated structures and avoid constructing queries by interpolating raw strings. The following examples illustrate secure patterns in Rust using common crates.

First, validate and sanitize input before using it in LDAP. Use a dedicated filter builder that escapes special characters or, better, avoids dynamic filter construction entirely. For MongoDB, use strongly typed documents and query builders instead of raw BSON strings.

use axum::{routing::post, Router};
use mongodb::{bson::{doc, oid::ObjectId}, Client};
use ldap3::{LdapConnAsync, Scope, SearchEntry};
use serde::{Deserialize, Serialize};

#[derive(Deserialize, Serialize)]
struct AuthRequest {
    username: String,
    password: String,
}

#[derive(Serialize)]
struct UserProfile {
    id: ObjectId,
    username: String,
    email: String,
}

/// Secure Axum handler example
async fn login_handler(
    body: axum::Json,
    ldap_uri: String,
    mongo_client: Client,
) -> Result, axum::http::StatusCode> {
    let username = sanitize_username(&body.username);
    // Constant-time bind to LDAP using parameterized filter
    let (ldap_conn, mut ldap) = LdapConnAsync::new(&ldap_uri).await.map_err(|_| axum::http::StatusCode::UNAUTHORIZED)?;
    let filter = format!("(uid={})", ldap_escape(&username));
    let (rs, _res) = ldap.search(
        "dc=example,dc=com",
        Scope::Subtree,
        &filter,
        vec!["mail"],
    ).await.map_err(|_| axum::http::StatusCode::UNAUTHORIZED)?;
    let mut ldap_success = false;
    for r in rs {
        if let Ok(SearchEntry { dn, attrs, .. }) = r {
            // Perform LDAP bind with password
            if ldap.simple_bind(&dn, &body.password).await.map_err(|_| axum::http::StatusCode::UNAUTHORIZED)?.success() {
                ldap_success = true;
            }
            break;
        }
    }
    if !ldap_success {
        return Err(axum::http::StatusCode::UNAUTHORIZED);
    }
    // Safe MongoDB query using typed document and validated username
    let db = mongo_client.database("appdb");
    let coll = db.collection::("users");
    let filter = doc! { "username": username };
    match coll.find_one(filter, None).await.map_err(|_| axum::http::StatusCode::INTERNAL_SERVER_ERROR)? {
        Some(profile) => Ok(axum::Json(profile)),
        None => Err(axum::http::StatusCode::UNAUTHORIZED),
    }
}

/// Basic sanitization: allow alphanumeric, underscore, hyphen; reject control chars
fn sanitize_username(input: &str) -> String {
    input.chars().filter(|c| c.is_alphanumeric() || *c == '_' || *c == '-').collect()
}

/// Escape LDAP special characters according to RFC 4515
fn ldap_escape(input: &str) -> String {
    let mut out = String::with_capacity(input.len() * 2);
    for ch in input.chars() {
        match ch {
            '*' => out.push_str(r"\2a"),
            '(' => out.push_str(r"\28"),
            ')' => out.push_str(r"\29"),
            '\\' => out.push_str(r"\5c"),
            '\x00'..='\x1f' | '\x7f' => out.push_str(&format!(r"\{:02x}", ch as u32)),
            _ => out.push(ch),
        }
    }
    out
}

/// Build a router with secure routes
fn app() -> Router {
    let client = Client::with_uri_str("mongodb://localhost:27017").unwrap();
    Router::new()
        .route("/login", post(move |body| login_handler(body, "ldap://ldap.example.com".to_string(), client.clone())))
}

Key points: sanitize usernames before using them in LDAP filters, use parameterized filters or escaping, and always use typed MongoDB documents for queries. Avoid building queries by string interpolation. middleBrick can scan your API definition and runtime behavior to highlight endpoints where LDAP and MongoDB inputs are not properly isolated, and it provides remediation guidance tied to frameworks such as OWASP API Top 10 and SOC2.