Cryptographic Failures in Fiber with Mongodb

Cryptographic failures occur when sensitive data is not adequately protected in transit or at rest. In a Fiber application using MongoDB as the backing store, the risk typically arises from application-level handling rather than the database protocol itself, but the interaction between the two can amplify exposure. A common pattern in Fiber handlers is to retrieve a user document from MongoDB and serialize it directly into JSON for an HTTP response. If the document contains sensitive fields such as password hashes, API keys, or internal identifiers, and the application does not explicitly omit or transform those fields, the data is effectively exposed in cleartext over TLS (or, worse, without TLS).

Consider a typical MongoDB document schema that includes a password_hash and a reset_token. A handler that uses collection.FindOne and returns the raw document to the client can unintentionally leak credentials or one-time tokens. Even when TLS is enforced, other vectors remain: logs, error messages, or client-side storage may retain sensitive fields. Additionally, if the application uses client-side encryption but stores encrypted blobs in MongoDB without proper key management, the cryptographic protection is nominal because the keys may be co-located with the data or embedded in source code.

Another scenario involves insecure default configurations in MongoDB deployments used during development. Binding to 0.0.0.0 without authentication or TLS on the database port allows on-path attackers to capture authentication handshakes and potentially decrypt traffic if weak ciphers are negotiated. In a Fiber service that connects to such a MongoDB instance, the cryptographic boundary is effectively absent, making any data exchanged between the app and the database readable to an attacker on the same network. This is a classic failure in transport-layer cryptography that maps directly to OWASP API Top 10 A02:2023 — Cryptographic Failures.

Real-world examples include CVE-2023-26133-like exposures where configuration errors lead to unencrypted MongoDB connections, and CVE-2021-3179-like patterns where sensitive fields are serialized without redaction. In both cases, the application’s responsibility is to enforce strict field-level handling and ensure encryption in use and at rest is properly managed, rather than relying on infrastructure defaults.

Remediation focuses on ensuring that sensitive fields are never returned to the client and that database connections are secured. Below are concrete Fiber handler examples that implement selective field projection and structured error handling to avoid cryptographic leakage.

1. Safe document retrieval with field projection in Fiber:

// main.go
package main

import (
	"context"
	"log"
	"net/http"

	"github.com/gofiber/fiber/v2"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

type User struct {
	ID       string `bson:"_id" json:"id"`
	Email    string `bson:"email" json:"email"`
	Password string `bson:"password_hash" json:"-"` // excluded from JSON
	Token    string `bson:"reset_token" json:"-"`   // excluded from JSON
}

func getUser(c *fiber.Ctx) error {
	client, err := mongo.Connect(c.Context(), options.Client().ApplyURI("mongodb://localhost:27017"))
	if err != nil {
		return c.Status(http.StatusInternalServerError).JSON(fiber.Map{"error": "database unavailable"})
	}
	defer client.Disconnect(c.Context())

	collection := client.Database("appdb").Collection("users")
	var user User
	// Use projection to return only safe fields
	filter := bson.D{{Key: "email", Value: c.Params("email")}
	projection := bson.D{{Key: "email", Value: 1}, {Key: "_id", Value: 1}}
	err = collection.FindOne(c.Context(), filter, options.FindOne().SetProjection(projection)).Decode(&user)
	if err != nil {
		if err == mongo.ErrNoDocuments {
			return c.Status(http.StatusNotFound).JSON(fiber.Map{"error": "user not found"})
		}
		return c.Status(http.StatusInternalServerError).JSON(fiber.Map{"error": "database error"})
	}
	return c.JSON(fiber.Map{"id" user.ID, "email" user.Email})
}

2. Enforcing TLS and authentication in MongoDB connection strings (for dev/test):

opts := options.Client().ApplyURI("mongodb://user:pass@localhost:27017/appdb?tls=true&tlsCAFile=/path/to/ca.pem&authMechanism=SCRAM-SHA-256")
client, err := mongo.Connect(context.TODO(), opts)

3. Middleware to strip sensitive headers and avoid logging leaks in Fiber:

func SecureMiddleware(c *fiber.Ctx) error {
	// Prevent sensitive headers from being logged by downstream systems
	c.Response().Header.Del(fiber.HeaderAuthorization)
	return c.Next()
}

These practices align with OWASP API Top 10 A02 and reduce the attack surface by ensuring that cryptographic protections are applied consistently across the stack.