Ldap Injection in Axum with Firestore

Ldap Injection occurs when an attacker can manipulate LDAP query construction by injecting malicious input. In an Axum application that uses Firestore as a data store, this typically appears in authentication or user-group lookup flows where user-supplied input is passed to an LDAP filter before Firestore is used to persist or retrieve related identity metadata. Because Axum does not provide built-in LDAP escaping, concatenating strings into LDAP filters creates an injection surface. Firestore may store user identities, group memberships, or mappings that an LDAP query references, and if those values are not validated, the combined flow becomes vulnerable.

Consider an endpoint that accepts a username and constructs an LDAP filter to locate the user, then retrieves additional profile data from Firestore. A vulnerable pattern looks like:

let username = form.username; // user-controlled
let filter = format("(&(objectClass=user)(sAMAccountName={}))", username);
// ldap.search(filter) ...
let doc = firestore.collection("users").doc(&username).get().await?;

Here, username is directly interpolated into the LDAP filter string. Attackers can supply values such as admin)(&(objectClass=user) to alter the filter logic, potentially bypassing authentication or enumerating directory entries. Even though Firestore is not responsible for LDAP parsing, the application’s reliance on user input across both systems means a weakness in one layer (LDAP query construction) can expose data stored in Firestore. For example, an attacker might manipulate the filter to return a different user’s Firestore document by leveraging group membership attributes retrieved via LDAP, leading to IDOR-like access across identity stores.

An API security scan using middleBrick would flag this as an authentication bypass and input validation issue, highlighting the risk when LDAP filters and Firestore document lookups share uncontrolled input. The scanner checks for missing allowlists, insufficient escaping, and unsafe consumption patterns that span multiple identity systems, emphasizing that securing only Firestore is insufficient when LDAP interactions are involved.

Remediation focuses on strict input validation, parameterized LDAP filter construction, and avoiding direct concatenation of user input. In Axum, use extractor validation and sanitize data before it reaches LDAP or Firestore. Prefer using an LDAP library that supports parameterized filters or implement strict allowlist rules for characters allowed in identifiers.

Below is a secure Axum handler that validates input, uses a parameterized approach for LDAP-like queries (via a library that supports placeholders), and safely retrieves Firestore data:

use axum::{routing::post, Router, extract::State};
use firestore::*; // hypothetical Firestore SDK wrapper
use serde::Deserialize;

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

async fn login_handler(
    State(db): State,
    axum::extract::Form(form): axum::extract::Form,
) -> Result<impl IntoResponse, (StatusCode, String)> {
    // Strict allowlist: only alphanumeric and limited symbols
    if !form.username.chars().all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '.') {
        return Err((StatusCode::BAD_REQUEST, "Invalid username".into()));
    }

    // Use a library that supports parameterized filters instead of string concat
    let ldap_filter = ldap_filter::build("objectClass=user")
        .eq("sAMAccountName", &form.username)
        .to_string();

    // Perform LDAP search (pseudocode)
    let ldap_users = ldap_search(&ldap_filter).await.map_err(|e| (StatusCode::UNAUTHORIZED, e.to_string()))?;
    if ldap_users.is_empty() {
        return Err((StatusCode::UNAUTHORIZED, "Invalid credentials".into()));
    }

    // Safe Firestore lookup using the validated identifier
    let user_ref = db.collection("users").doc(&form.username);
    let profile: UserProfile = user_ref.get().await.map_err(|e| (StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    // Continue authentication logic...
    Ok(Json(LoginResponse { ok: true }))
}

Key points:

• Input validation: A character-level allowlist prevents special LDAP metacharacters (such as *, (, ), &) from reaching the LDAP filter.
• Parameterized filters: Using an LDAP helper that supports placeholders ensures user input is treated as data, not part of the query syntax.
• Firestore document path safety: Even after LDAP validation, treat Firestore document IDs as opaque and avoid path traversal via characters like / or . that could affect namespacing.

For production, combine this with rate limiting and monitoring. middleBrick’s scans can verify that no user input reaches LDAP or Firestore without validation, and the Pro plan’s continuous monitoring can alert you if new endpoints introduce similar patterns.