Ldap Injection in Aspnet with Firestore

Ldap Injection occurs when an attacker can manipulate LDAP query construction, typically by injecting special characters such as *, (, ), &, or | into input that is concatenated into an LDAP filter string. In an Aspnet application that uses Firestore as a data store but still performs LDAP operations (for example, to validate credentials or group membership), unsafe construction of LDAP filters can expose authentication and authorization logic even though Firestore itself does not execute LDAP queries.

Consider an Aspnet service that stores user profiles in Firestore and uses an on-premises LDAP directory for authentication. If the application builds an LDAP filter by string concatenation, for example:

string username = userInput; // unsanitized
string filter = $"(uid={username})";
var searchRequest = new SearchRequest("ou=people,dc=example,dc=com", filter, ...);

An attacker providing )(uid=foo) as username can modify the filter logic, potentially bypassing authentication or extracting additional data via crafted responses. This becomes a chain-of-trust issue: Firestore may hold user mappings (e.g., mapping a Firestore document ID to an LDAP DN), and an injection point in LDAP can allow privilege escalation or information disclosure.

Firestore-specific aspects come into play when Firestore data is used to build or select LDAP targets. For instance, if an Aspnet controller retrieves a Firestore document to obtain an LDAP distinguished name (DN) or group membership before querying LDAP, and those values are concatenated without validation, the Firestore-supplied data can itself be leveraged in an injection chain. A malicious actor might attempt to manipulate stored Firestore fields (if write paths are insufficiently guarded) or exploit trust in Firestore-retrieved identifiers to steer LDAP queries into unintended branches of the directory tree.

Moreover, because middleBrick tests such scenarios by running parallel checks including Authentication and BOLA/IDOR, it can surface cases where LDAP logic depends on Firestore-derived identifiers without adequate input validation or output encoding. The presence of an unauthenticated LLM endpoint is not relevant here; the risk is in how the Aspnet layer composes LDAP filters and how Firestore data participates in that composition.

Remediation focuses on never concatenating user or Firestore-derived data directly into LDAP filters. Use parameterized LDAP filters or an LDAP filter builder that properly escapes special characters. In Aspnet, treat LDAP queries like SQL queries: use parameters or an abstraction that enforces safe encoding.

Example of unsafe code to avoid:

// UNSAFE: string concatenation in LDAP filter
string userSupplied = Request.Query["username"];
string firestoreDn = GetFirestoreDocumentField(userId, "ldapDn"); // e.g., "uid=alice,ou=people,dc=example,dc=com"
string filter = $"(&(objectClass=user)(distinguishedName={firestoreDn})(cn={userSupplied}))";

Safe approach using System.DirectoryServices.Protocols escaping and parameterization:

// SAFE: use proper escaping and avoid concatenation of untrusted data into the filter
using System.DirectoryServices.Protocols;

string userSupplied = Request.Query["username"];
string firestoreDn = GetFirestoreDocumentField(userId, "ldapDn");

// Escape user-supplied components for use in an LDAP filter substring
string escapedUser = LdapFilter.EscapeFilter(userSupplied);
string escapedDn = LdapFilter.EscapeFilter(firestoreDn);

// Use parameterized-style composition; build a filter that does not rely on injection-prone concatenation
string filter = $"(uid={escapedUser})";
var request = new SearchRequest(
    $"ou=people,dc=example,dc=com",
    filter,
    SearchScope.Subtree,
    null
);
// If you must incorporate a DN, prefer a direct bind or a controlled lookup rather than embedding in filter

Firestore-specific validation before use:

// Validate Firestore-derived values before they influence LDAP logic
string firestoreDn = GetFirestoreDocumentField(userId, "ldapDn");
if (!IsValidDn(firestoreDn)) {
    throw new SecurityException("Invalid directory reference.");
}

bool IsValidDn(string dn)
{
    // Basic structural check; tailor to your directory schema
    return !string.IsNullOrWhiteSpace(dn)
        && dn.StartsWith("uid=", StringComparison.OrdinalIgnoreCase)
        && dn.Contains(",dc=");
}

Additional protections: enforce strict input validation on all user-controlled fields, apply the principle of least privilege for the service account used by Aspnet to bind to LDAP, and log and monitor anomalous queries. middleBrick can detect insecure LDAP filter construction and weak validation practices through its parallel security checks, providing prioritized findings with remediation guidance.