Ldap Injection in Express with Dynamodb

Ldap Injection in an Express application that uses DynamoDB as a data store occurs when user-controlled input is passed into LDAP query-building logic without validation or escaping. DynamoDB itself does not interpret LDAP queries, so the database layer does not introduce the injection. Instead, the vulnerability arises in the Express route handlers where input is concatenated into LDAP filter strings before any DynamoDB operations are considered. An attacker can manipulate parameters such as username or search to alter the semantics of the LDAP filter, potentially bypassing authentication or extracting directory data.

Consider an Express endpoint that authenticates a user by searching an LDAP directory and then retrieves additional profile attributes from DynamoDB. If the LDAP filter is built using string concatenation, a payload like username=admin)(objectClass=*) can change the filter from a targeted search to a broad match. Successful LDAP manipulation may return an attacker’s chosen identity token, which the application then uses to look up a corresponding item in DynamoDB using a predictable key (e.g., the attacker-supplied username). Even though DynamoDB stores safe, structured data, the earlier LDAP injection grants unauthorized access to the lookup path, leading to authentication bypass or information disclosure. This combination highlights a design where untrusted input influences directory queries before any DynamoDB access control is applied.

The risk is compounded when the Express service queries DynamoDB using the attacker-influenced identifier without additional authorization checks. For example, after a manipulated LDAP bind succeeds, the application might call GetItem with a user-supplied userId to fetch permissions. If the LDAP step did not properly validate identity, an attacker can enumerate valid user IDs or elevate privileges by exploiting gaps between LDAP group membership and DynamoDB role mappings. Because the scan tests authentication, BOLA/IDOR, and input validation concurrently, such cross-layer weaknesses are detectable when the API’s unauthenticated surface includes both LDAP-dependent endpoints and DynamoDB-backed resources.

Tools that perform black-box scanning without credentials can identify these patterns by observing inconsistent authentication outcomes and malformed filter handling. The presence of LDAP-related endpoints alongside DynamoDB-driven authorization logic increases the attack surface. The scanner’s authentication, input validation, and property authorization checks can surface indicators such as missing sanitization on distinguished name (DN) components and over-permissive read paths in DynamoDB. Remediation requires strict input validation for all LDAP filter components and explicit mapping between authenticated identity and DynamoDB access, ensuring that directory manipulation cannot bypass application-level authorization.

To remediate Ldap Injection in Express while interacting with DynamoDB, you must validate and sanitize all inputs used in LDAP filters and enforce strict identity-to-DynamoDB mapping. Use parameterized filter construction or an LDAP library that supports safe escaping, and avoid string interpolation for queries. For DynamoDB, apply least-privilege IAM policies so that the authenticated user or role can only access items they are entitled to, and validate ownership server-side before any read or write.

Below is a secure Express pattern that separates LDAP authentication from DynamoDB profile retrieval. The LDAP filter uses an ldap-filter helper to escape special characters, preventing injection. After a successful bind, the application derives the DynamoDB key from the verified bind identity rather than from user input, eliminating IDOR risks.

const express = require('express');
const { LDAPClient } = require('ldapjs');
const { DynamoDBDocumentClient, GetCommand } = require('@aws-sdk/lib-dynamodb');
const { ldapFilter } = require('ldap-filter');

const app = express();
const client = new LDAPClient({ url: 'ldap://directory.example.com' });
const ddb = DynamoDBDocumentClient.from(new AWS.DynamoDB());

app.get('/profile', async (req, res) => {
  const { username } = req.query;

  // Validate and sanitize input
  if (!username || typeof username !== 'string') {
    return res.status(400).json({ error: 'Invalid username' });
  }

  // Build safe LDAP filter
  const filter = ldapFilter.encode({ attribute: 'uid', value: username });
  const searchDN = 'ou=people,dc=example,dc=com';
  const opts = { filter };

  try {
    await client.bind(); // anonymous or service account bind for search
    const searchResult = await client.search(searchDN, opts);
    if (!searchResult || searchResult.items.length === 0) {
      return res.status(401).json({ error: 'Invalid credentials' });
    }

    // Use the verified identity for DynamoDB lookup
    const verifiedUid = searchResult.items[0].uid;
    const cmd = new GetCommand({
      TableName: 'Users',
      Key: { userId: verifiedUid }
    });
    const { Item } = await ddb.send(cmd);

    if (!Item) {
      return res.status(404).json({ error: 'Profile not found' });
    }

    res.json({ profile: Item });
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Internal error' });
  } finally {
    await client.unbind();
  }
});

If you use an ORM or SDK that does not expose filter escaping, prefer whitelisting allowed characters for identifiers and reject inputs containing parentheses, asterisks, or backslashes. For DynamoDB, always scope GetItem or Query operations to the authenticated subject. The following example demonstrates a defensive check that the requesting user matches the target item, preventing horizontal IDOR even when an indirect reference is supplied.

app.get('/users/:userId', async (req, res) => {
  const requestingUserId = req.verifiedUserId; // from LDAP bind
  const targetUserId = req.params.userId;

  if (requestingUserId !== targetUserId) {
    return res.status(403).json({ error: 'Forbidden' });
  }

  const cmd = new GetCommand({
    TableName: 'Users',
    Key: { userId: targetUserId }
  });
  const { Item } = await ddb.send(cmd);
  res.json({ profile: Item || {} });
});

These fixes ensure that LDAP queries cannot be altered by malicious input and that DynamoDB access is constrained to the authenticated identity. The scanner’s checks for authentication, input validation, and property authorization will reflect reduced risk when such patterns are in place.