Ldap Injection with Bearer Tokens

LDAP injection attacks targeting Bearer Token implementations exploit the way authentication systems construct LDAP queries using token-derived claims or user identifiers. When a Bearer Token contains claims like usernames, email addresses, or organizational identifiers, and these values are directly interpolated into LDAP search filters without proper sanitization, attackers can manipulate the query structure to bypass authentication or extract sensitive directory information.

A common vulnerability pattern occurs when applications extract the subject (sub) claim from JWT tokens and use it directly in LDAP filters. For example, a filter like (uid=username) becomes dangerous when username contains LDAP metacharacters. An attacker submitting a token with uid=admin)(|(uid=* in the sub claim transforms the filter into (uid=admin)(|(uid=*), which evaluates as a logical OR condition, potentially returning multiple user entries or bypassing intended access controls.

Another critical vector involves organizational or group-based authorization. When tokens carry group membership claims that are used to construct filters like (member=group), an attacker can inject OR clauses to include any group they choose. This becomes especially dangerous in multi-tenant systems where group membership determines data access boundaries.

LDAP injection in Bearer Token contexts also manifests through attribute-based searches. If applications use token claims to search for user attributes like email or phone number, and these values contain special characters like *, (, ), or , the LDAP query can be manipulated to perform wildcard searches, return unintended results, or even cause denial of service through malformed queries.

Detecting LDAP injection vulnerabilities in Bearer Token implementations requires both static analysis and dynamic testing approaches. Static analysis should focus on code paths where token claims are extracted and used in LDAP operations. Look for patterns where JWT claims are directly concatenated into filter strings without validation or encoding.

Dynamic testing involves submitting tokens with crafted claims containing LDAP metacharacters and observing the system's behavior. A simple test involves creating a token with the sub claim set to admin)(uid=* and monitoring whether the authentication succeeds or returns unexpected user information. If the system authenticates as a different user than expected, LDAP injection is likely present.

middleBrick's scanning approach for this specific vulnerability includes testing the unauthenticated attack surface by submitting tokens with various LDAP injection payloads to authentication endpoints. The scanner attempts to bypass authentication by injecting OR conditions, wildcard searches, and null byte injections. For each test, middleBrick monitors the response for signs of successful authentication bypass, information disclosure, or error messages that reveal directory structure.

Effective detection also requires examining error handling. When LDAP injection attempts cause directory service errors, the error messages should never reveal internal directory structure, attribute names, or query syntax details. Systems that return detailed LDAP error messages provide attackers with valuable information for crafting more sophisticated injection attacks.

API endpoints that accept Bearer Tokens for authentication should be tested with tokens containing various LDAP special characters: (, ), &, |, *, , and null bytes. The scanner should verify that these characters are either rejected with appropriate error messages or properly escaped before being used in LDAP operations.

Remediating LDAP injection vulnerabilities in Bearer Token implementations requires a defense-in-depth approach. The most effective strategy combines input validation, proper escaping, and architectural changes to eliminate unsafe query construction patterns.

Input validation should enforce strict character whitelisting on token claims used in LDAP operations. For usernames, allow only alphanumeric characters, underscores, and hyphens. For email addresses, use standard email validation patterns. Any claim containing special characters should be rejected with a clear error message rather than attempting to sanitize or escape the input.

// Secure claim validation before LDAP use
function validateLdapSafeClaim(claim, claimName) {
  const emailPattern = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
  const usernamePattern = /^[a-zA-Z0-9_-]+$/;
  
  if (claimName === 'email' && !emailPattern.test(claim)) {
    throw new Error('Invalid email format in token claim');
  }
  
  if (claimName === 'username' && !usernamePattern.test(claim)) {
    throw new Error('Invalid username format in token claim');
  }
  
  return claim;
}

Proper escaping is essential when claims cannot be validated against strict patterns. Use the directory service's built-in escaping mechanisms rather than custom escaping logic. For LDAP, this means replacing ( with \28, ) with \29, * with \2a, and other special characters with their escaped equivalents.

// LDAP metacharacter escaping
function escapeLdapFilter(value) {
  const escapeMap = {
    '\\': '\\5c',
    '*': '\\2a',
    '(': '\\28',
    ')': '\\29',
    '\u0000': '\\00',
    '/': '\\2f'
  };
  
  return value.replace(/[\\*\(\)\\u0000\/]/g, char => escapeMap[char]);
}

// Usage with LDAP filters
const token = jwt.verify(tokenString, secret);
const escapedUid = escapeLdapFilter(token.sub);
const filter = `(uid=${escapedUid})`;

Architectural remediation involves eliminating direct string concatenation in LDAP queries entirely. Use parameterized LDAP queries or search controls that separate query structure from user data. This approach ensures that user-supplied values cannot alter the query's logical structure, regardless of their content.

Consider implementing claim-based access control that doesn't rely on LDAP queries for authorization decisions. Store authorization information in the token itself or use a separate authorization service that doesn't construct LDAP filters from user input. This reduces the attack surface and eliminates the LDAP injection vector entirely.

Regular security testing should include automated scanning of all API endpoints that accept Bearer Tokens. middleBrick's continuous monitoring can detect when new LDAP injection vulnerabilities are introduced through code changes, ensuring that remediation efforts remain effective over time.