Ldap Injection in Fiber with Jwt Tokens

LDAP injection occurs when an attacker can manipulate LDAP query construction through untrusted input. In a Fiber application that uses JWT tokens for authentication, risk emerges not from JWT parsing itself, but from how claims or parameters extracted from the token are later used to build LDAP filters or DN strings. If the application deserializes a JWT, extracts a user identifier (such as uid or email), and directly interpolates that value into an LDAP search filter without validation or escaping, the attacker may supply crafted JWT claims to inject LDAP filter syntax.

Consider a scenario where a Fiber route authenticates a user via a JWT access token and then queries an LDAP directory to retrieve group memberships. An attacker who can influence the JWT (via a weak signing algorithm, token leakage, or a malicious issuer in a misconfigured setup) can embed LDAP metacharacters in a claim. For example, a username claim of (|(objectClass=person)(objectClass=organizationalPerson)) would break the intended filter structure. If the application builds the filter with string concatenation, the injected content can change the filter semantics, potentially bypassing authorization checks or causing excessive LDAP queries that lead to denial of service.

Another specific combination involves using JWTs to convey tenant or scope identifiers that are used in DN construction. If the application builds DNs by concatenating a user-provided value from the JWT with a base DN, an attacker can supply values like CN=attacker,DC=example,DC=com or escape sequences to traverse the directory tree. This can expose objects the user should not access or enable privilege escalation if the application assumes DNs are trustworthy. Because JWTs are often treated as trusted identity tokens, developers may skip input validation for claims used in LDAP operations, inadvertently creating a path for LDAP injection.

Furthermore, the interaction with middleware that verifies JWTs can obscure the origin of untrusted data. If authorization decisions are made based on token claims and later those claims are used in LDAP queries without re-sanitization, the security boundary between authentication and data access is blurred. Attackers may probe endpoints with modified JWTs to observe differences in behavior, timing, or error messages, which can reveal whether LDAP injection is feasible. The risk is compounded when the application reflects LDAP errors in HTTP responses, providing feedback that assists in crafting injection payloads.

To detect this class of issue, scanners check whether claims from JWTs are used in constructing LDAP filters or DNs, and whether they are properly sanitized or parameterized. Findings are mapped to the OWASP API Top 10 and relevant compliance frameworks to highlight the severity of improper user data usage in directory operations. Because LDAP injection can lead to unauthorized data access or bypass of access controls, addressing it is essential for applications that integrate identity tokens with directory services.

Remediation focuses on strict validation, parameterized LDAP queries, and avoiding direct string interpolation of JWT-derived values. When using JWT tokens in Fiber, treat all claims as untrusted for directory operations. Use allowlists for known claim values, enforce length and pattern constraints, and prefer using an LDAP library that supports parameterized filters rather than building filter strings manually.

Below is a secure example of extracting a claim from a JWT and using it in an LDAP search with proper escaping. The code uses the github.com/golang-jwt/jwt/v5 package for parsing and github.com/go-ldap/ldap/v3 for constructing safe filters. Note that the username claim is validated against a regex pattern before use, and the filter is built with ldap.NewFilterControlSubstrings to prevent injection.

// Example: secure handling of JWT claims for LDAP queries in Fiber
package main

import (
	"github.com/gofiber/fiber/v2"
	"github.com/golang-jwt/jwt/v5"
	"github.com/go-ldap/ldap/v3"
)

func validateUsername(username string) bool {
	// Allow only alphanumeric and limited special characters typical in usernames
	// Adjust pattern to match your organization’s naming rules
	matched, _ := regexp.MatchString(`^[a-zA-Z0-9._-]{1,64}$`, username)
	return matched
}

func buildLDAPFilter(username string) (*ldap.Filter, error) {
	// Use parameterized substrings to avoid injection
	filter, err := ldap.NewFilterControlSubstrings(
		ldap.NewEqualityMatchFilter("uid", username),
	)
	if err != nil {
		return nil, err
	}
	return filter, nil
}

func setupRoutes(app *fiber.App) {
	app.Get("/members", func(c *fiber.Ctx) error {
		auth := c.Get("Authorization")
		if auth == "" {
			return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "missing authorization header"})
		}

		tokenString := auth[len("Bearer "):]
		token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
			// validate signing method and return appropriate key
			return []byte("your-secret-key"), nil
		})
		if err != nil || !token.Valid {
			return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid token"})
		}

		if claims, ok := token.Claims.(jwt.MapClaims); ok && token.Valid {
			username, ok := claims["username"].(string)
			if !ok || !validateUsername(username) {
				return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "invalid username claim"})
			}

			ldapFilter, err := buildLDAPFilter(username)
			if err != nil {
				return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "failed to build LDAP filter"})
			}

			// Use ldapFilter in your LDAP search; do not concatenate strings
			searchRequest := ldap.NewSearchRequest(
				"dc=example,dc=com",
				ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
				ldapFilter.String(),
				[]string{"cn", "mail"},
				nil,
			)
			// Perform LDAP search with client.search(...) here
			return c.JSON(fiber.Map{"filter": ldapFilter.String()})
		}
		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "invalid claims"})
	})
}

Additional remediation steps include enforcing strict JWT validation (issuer, audience, expiration), using short-lived tokens, and applying the principle of least privilege to LDAP service accounts. Avoid logging raw JWT claims or LDAP errors that could aid an attacker. Regularly rotate secrets and review token validation logic to reduce the attack surface.