Ldap Injection in Actix with Dynamodb

Ldap Injection occurs when untrusted input is concatenated into an LDAP query without validation or escaping. In an Actix web service that uses an LDAP server for authentication or group lookups, user-controlled strings such as usernames or search filters can alter the query logic. When the same Actix application stores or references user data in Amazon DynamoDB, the identity store becomes part of the trust boundary: attacker-controlled values submitted to Actix may be written to or read from DynamoDB and later used in LDAP filters.

Consider an Actix handler that accepts a username parameter, looks up the user in DynamoDB to retrieve an employee ID, and then performs an LDAP search using that ID to build a filter like (&(employeeId={id})(objectClass=person)). If the DynamoDB item contains an employeeId derived from unsanitized input (for example, an attacker-supplied string), the resulting LDAP filter becomes injectable. Special characters such as asterisk *, parentheses, and NUL bytes can change the filter semantics, enabling unauthorized authentication or data extraction. The DynamoDB read in Actix does not validate or sanitize the attribute before it is used in LDAP, turning a typical NoSQL lookup into an injection vector.

An example flow: an attacker sends a crafted request to the Actix endpoint with username=admin*. DynamoDB stores this value in an attribute used later in the LDAP filter. When Actix builds the LDAP query, the wildcard expands the match, potentially returning multiple entries or bypassing intended access controls. Because the scan testing in middleBrick evaluates unauthenticated attack surfaces, such cross-service injection paths—between DynamoDB and LDAP—are surfaced as high-severity findings under BFLA/Privilege Escalation and Input Validation checks.

Remediation focuses on strict input validation, parameterized queries, and avoiding direct concatenation of DynamoDB attributes into LDAP filters. In Actix, validate and sanitize all user inputs before they are written to or read from DynamoDB. Use strongly typed structures and avoid building LDAP filters by string interpolation.

1. Validate input and use prepared patterns

Reject or transform characters that have special meaning in LDAP filters. For employee IDs, enforce a strict pattern (e.g., alphanumeric and underscores) and length limits before storing them in DynamoDB.

use actix_web::{web, HttpResponse, Result};
use regex::Regex;

fn is_valid_employee_id(value: &str) -> bool {
    let re = Regex::new(r"^[a-zA-Z0-9_]{1,64}$").unwrap();
    re.is_match(value)
}

async fn get_user_data(form: web::Form<UserForm>) -> Result<HttpResponse> {
    if !is_valid_employee_id(&form.employee_id) {
        return Ok(HttpResponse::BadRequest().body("Invalid employee ID"));
    }
    // safe to proceed
    Ok(HttpResponse::Ok().finish())
}

2. Use DynamoDB condition expressions and parameterized attribute values

When reading from DynamoDB in Actix, use the AWS SDK for Rust with expression attribute values to avoid injection through attribute values. Do not embed raw attribute values into LDAP filters.

use aws_sdk_dynamodb::types::AttributeValue;
use aws_sdk_dynamodb::Client;

async fn fetch_employee(client: &Client, employee_id: &str) -> Option<String> {
    let resp = client
        .get_item()
        .table_name("Employees")
        .key(
            "employeeId",
            AttributeValue::S(employee_id.to_string()),
        )
        .send()
        .await
        .ok()
        .and_then(|out| out.item().and_then(|item| item.get("employeeId").cloned().map(|v| v.as_s().unwrap_or(&"").to_string())));
    resp
}

3. Build LDAP filters safely with parameterized placeholders

When constructing LDAP search filters, use a library that escapes special characters or build filters with explicit placeholders. Never concatenate DynamoDB attribute values directly into the filter string.

use ldap3::LdapConnAsync;
use ldap3::result::Result as LdapResult;

async fn safe_ldap_search(employee_id: &str) -> LdapResult<()> {
    // Assume ldap_conn is an established LdapConnAsync
    let mut ldap_conn = LdapConnAsync::new("ldap://localhost").await?;
    // Escape special characters according to RFC 4515
    let filter = format!("(employeeId={})", ldap_escape::escape(employee_id));
    ldap_conn.search(
        "dc=example,dc=com",
        ldap3::Scope::Subtree,
        &filter,
        vec!["cn"],
    ).await?.success()?;
    Ok(())
}

4. Defense-in-depth: schema design and runtime checks

Design DynamoDB tables to separate identity attributes used in LDAP from mutable user input. Enforce attribute constraints at the DynamoDB level where possible (e.g., numeric IDs with no special characters). In Actix, apply middleware that audits outgoing data to ensure no raw LDAP filter fragments are constructed from untrusted sources.

middleBrick findings for this scenario highlight Input Validation and BFLA/Privilege Escalation checks, emphasizing the need for parameterized handling across services. Remediation guidance provided by the scanner aligns with OWASP API Top 10 A01 and A07, ensuring that fixes map to recognized compliance frameworks.