Jwt Misconfiguration in Fiber with Dynamodb

JWT misconfiguration in a Fiber application that uses DynamoDB as a user or session store can expose authentication bypass or privilege escalation risks. Common issues include missing or weak signature verification, overly permissive token claims, and insecure storage or handling of secrets. When combined with DynamoDB, misconfiguration can amplify the impact: for example, if the application uses predictable or missing partition keys, or accidentally exposes tokens or secrets in logs or backups, an attacker who gains access to a token can more easily map or traverse user identities in DynamoDB.

In a black-box scan, middleBrick tests unauthenticated endpoints and inspects how tokens are validated, stored, and referenced. If endpoints rely on incomplete token validation before querying DynamoDB (for example, using a token’s sub or username claim directly as a DynamoDB key without ensuring it matches the authenticated user), this can lead to Insecure Direct Object References (IDOR) or Broken Object Level Authorization (BOLA). middleBrick checks whether JWT claims are properly bound to the underlying DynamoDB item ownership and whether authorization checks occur on every request.

Specific patterns that increase risk include: using unsigned tokens (alg none), not validating the iss and aud claims, storing sensitive metadata in token payloads that get logged, and using static or weak signing keys that can be guessed or extracted. If the application stores refresh tokens or session metadata in DynamoDB with insufficient access controls, a leaked token can lead to unauthorized reads or updates. middleBrick’s JWT/AI Security checks also look for system prompt leakage and prompt injection in any AI-assisted components that may interact with authentication flows, ensuring AI tooling does not expose or manipulate tokens.

To secure JWT usage with DynamoDB in Fiber, enforce strict token validation, bind tokens to DynamoDB item ownership, and avoid exposing sensitive data in logs or keys. Use the official AWS SDK for Go and the middleware provided by Fiber to validate JWTs before any DynamoDB call.

1. Validate JWT and bind to DynamoDB item ownership

Always verify the token signature, issuer, audience, and expiration before using any claims to construct DynamoDB queries. Use the token’s subject (sub) to parameterize queries rather than accepting user-supplied identifiers.

// main.go
package main

import (
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/jwt"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
	"context"
	"fmt"
)

func main() {
	app := fiber.New()

	config, _ := config.LoadDefaultConfig(context.TODO(), config.WithRegion("us-west-2"))
	db := dynamodb.NewFromConfig(config)

	app.Use("/api/*", jwt.New(jwt.Config{
		SigningKey: jwt.SigningKey{Key: []byte(os.Getenv("JWT_SECRET"))},
		ContextKey: "user",
	}))

	app.Get("/api/profile", func(c *fiber.Ctx) error {
		user := c.Locals("user").(*jwt.Token)
		claims := user.Claims.(jwt.StandardClaims)

		// Use the token subject as the partition key to ensure users only access their own item
		input := &dynamodb.GetItemInput{
			TableName: aws.String(os.Getenv("DYNAMO_TABLE")),
			Key: map[string]types.AttributeValue{
				"PK": &types.AttributeValueMemberS{Value: fmt.Sprintf("USER#%s", claims.Subject)},
			},
		}

		out, err := db.GetItem(c.Context(), input)
		if err != nil || out.Item == nil {
			return c.Status(fiber.StatusNotFound).SendString("not found")
		}
		return c.JSON(out.Item)
	})

	app.Listen(":3000")
}

2. Use strong key material and avoid logging secrets

Rotate signing keys, avoid storing raw secrets in environment files that are backed up or logged, and ensure DynamoDB item keys do not contain raw tokens. Prefer opaque identifiers mapped server-side.

// Example: safe token generation and DynamoDB write
import (
	"github.com/gofiber/fiber/v2/middleware/jwt"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/google/uuid"
)

func createUserSession(c *fiber.Ctx, db *dynamodb.Client, userID string) error {
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
		"sub": userID,
		"jti": uuid.NewString(),
		"exp": time.Now().Add(time.Hour * 24).Unix(),
	})
	signed, _ := token.SignedString([]byte(os.Getenv("JWT_SECRET")))

	// Store only a mapping key, not the token itself
	_, err := db.PutItem(c.Context(), &dynamodb.PutItemInput{
		TableName: aws.String(os.Getenv("DYNAMO_TABLE")),
		Item: map[string]types.AttributeValue{
			"PK": &types.AttributeValueMemberS{Value: fmt.Sprintf("SESSION#%s", userID)},
			"SK": &types.AttributeValueMemberS{Value: signed[:8]}, // store a fragment only
		},
	})
	return err
}

3. Enforce least-privilege IAM and validate input

Ensure the IAM role used by Fiber has least-privilege access to DynamoDB and that input validation prevents injection or malformed keys. Do not rely on client-supplied keys alone.

// Validate key format before querying
if !regexp.MustCompile(`^USER#[a-zA-Z0-9_-]+$`).MatchString(claims.Subject) {
	return c.SendStatus(fiber.StatusBadRequest)
}