Ldap Injection in Fiber with Hmac Signatures

LDAP Injection is an injection-based attack where untrusted input is concatenated into LDAP query strings, allowing an attacker to alter query logic or bypass authentication. In a Fiber application that uses Hmac Signatures for request integrity, combining weak input handling with signature verification can still expose authentication and authorization risks.

Consider a login handler that builds an LDAP filter from a username parameter and then validates an Hmac Signature sent in a header. If the username is directly interpolated into the filter without escaping, an attacker can inject crafted characters (e.g., * or )) to change the semantics of the LDAP query. Even when the request carries a valid Hmac Signature, the backend may treat the signature as proof of integrity and origin, leading to implicit trust in the manipulated query. For example, an attacker-supplied username like admin)(|(objectClass=*) could bypass intended filters, potentially returning unintended entries or authenticating as another user if the server’s LDAP library does not enforce strict parsing controls.

Hmac Signatures are designed to ensure that the request payload and headers have not been altered in transit. In Fiber, developers often compute the Hmac over selected headers and the body, then compare it to a signature provided by the client. If the server uses a vulnerable LDAP query that reflects injected content, the signature validation may pass while the backend executes the malicious query. This creates a scenario where integrity checks do not protect against logic tampering: the signature covers the attacker-controlled input, and the server processes it unsafely. Moreover, if the Hmac key is leaked or predictable, an attacker could forge valid signatures for injected payloads, compounding the risk. Although the scan checks do not test for LDAP-specific logic, they can identify missing input validation and weak authorization checks that coexist with Hmac usage, highlighting where an attacker might leverage LDAP Injection despite signature verification.

Real-world patterns include using the Compare method for Hmac validation to avoid timing leaks and ensuring that user-controlled data never directly forms the LDAP filter. Frameworks like Fiber provide context objects where parameters should be sanitized before use, and developers should treat LDAP queries as strictly structured rather than freeform strings. Integrating middleBrick’s checks can surface gaps where signature validation exists but input validation and query construction remain weak, guiding more robust design that keeps authentication logic and integrity checks properly separated.

Remediation focuses on strict input validation, safe query construction, and disciplined Hmac usage. Never build LDAP filters by concatenating raw user input. Instead, use parameterized approaches or dedicated libraries that escape special characters. Validate the format of identifiers (e.g., allow only safe characters for usernames) and enforce length and character restrictions before any cryptographic operations.

When computing Hmac Signatures in Fiber, use the standard library to avoid implementation errors. Compute the signature over a canonical representation of the request elements you intend to protect, and compare signatures using a constant-time function to prevent timing attacks. Keep the Hmac key out of source code and manage it via secure configuration or secret management. Below are concrete, working examples that demonstrate secure handling in a Fiber-based service.

Example 1: Hmac Validation with Safe Input Handling

const crypto = require('crypto');
const { app, request } = require('fibers/fiber');

const HMAC_KEY = process.env.HMAC_KEY; // Load from secure configuration

function computeHmac(headers, body) {
  const message = headers['date'] + '|' + body;
  return crypto.createHmac('sha256', HMAC_KEY).update(message).digest('hex');
}

app.post('/login', (req, res) => {
  const receivedSignature = req.get('X-Request-Signature');
  if (!receivedSignature) {
    return res.status(400).send({ error: 'Missing signature' });
  }

  const expectedSignature = computeHmac({
    date: req.get('Date') || req.get('date'),
  }, req.body);

  const valid = crypto.timingSafeEqual(
    Buffer.from(receivedSignature, 'hex'),
    Buffer.from(expectedSignature, 'hex')
  );

  if (!valid) {
    return res.status(401).send({ error: 'Invalid signature' });
  }

  // Proceed with sanitized input
  const safeUsername = req.body.username.replace(/[^a-zA-Z0-9._-]/g, '').substring(0, 64);
  if (!safeUsername) {
    return res.status(400).send({ error: 'Invalid username' });
  }

  // Build LDAP filter safely; do not interpolate raw input
  const ldapFilter = `(&(objectClass=user)(uid=${safeUsername}))`;
  // Use ldapFilter with a vetted LDAP library
  res.send({ status: 'ok' });
});

Example 2: Structured Query Building and Signature Scope

const crypto = require('crypto');
const { Router } = require('fibers/router');
const router = Router();

const HMAC_KEY = process.env.HMAC_KEY;

function buildCanonicalString(headers, sanitizedBody) {
  // Include only headers you intend to protect
  return [headers.date, sanitizedBody].join('|');
}

router.post('/resource', (req, res) => {
  // Validate and sanitize inputs before using them
  const id = req.params.id;
  if (!/^[a-f0-9]{24}$/.test(id)) {
    return res.status(400).send({ error: 'Invalid ID' });
  }

  const sanitizedBody = JSON.stringify({
    action: req.body.action,
    target: req.body.target.replace(/[^\w-]/g, ''),
  });

  const signature = crypto.createHmac('sha256', HMAC_KEY)
    .update(buildCanonicalString({ date: req.get('Date') }, sanitizedBody))
    .digest('hex');

  const provided = req.get('X-Request-Signature');
  if (!provided || !crypto.timingSafeEqual(Buffer.from(signature, 'hex'), Buffer.from(provided, 'hex'))) {
    return res.status(401).send({ error: 'Invalid signature' });
  }

  // Use sanitized parameters in any backend logic, avoiding raw concatenation in LDAP queries
  res.send({ id, status: 'processed' });
});

These examples emphasize canonical message construction, constant-time comparison, and strict sanitization before query assembly. They align with practices that reduce the likelihood of injection while preserving the integrity guarantees offered by Hmac Signatures. middleBrick can complement these efforts by validating that input checks and signature scopes are present and correctly implemented, surfacing misconfigurations where Hmac usage exists alongside unsafe query construction.