Token Leakage in Fiber with Jwt Tokens

Token leakage in applications built with the Fiber web framework when using JWT tokens typically occurs through insecure exposure of tokens in logs, error messages, URLs, or headers. Because Fiber is a fast, Express-like web framework written in Go, developers may inadvertently expose JWTs in several ways:

• Logging request details that include authorization headers containing JWTs, writing bearer tokens to application or server logs in plaintext.
• Returning JWTs or sensitive user data within HTTP responses or error payloads, for example in detailed validation error messages.
• Using query parameters or URL fragments to pass tokens, which can be stored in server logs, browser history, or referrer headers.
• Misconfigured CORS or insecure cookie attributes (e.g., missing Secure or HttpOnly) when storing JWTs in cookies, enabling leakage to unauthorized origins or client-side scripts.
• Improper handling of token refresh flows where short-lived access tokens are extended or persisted insecurely, increasing the window for exposure.

In a black-box scan using middleBrick, these practices can be detected through checks such as Data Exposure and Unsafe Consumption. For example, if a Fiber endpoint returns a JWT in a JSON response body or includes it in an error stack trace, middleBrick can flag this as a finding with severity and remediation guidance. Similarly, if request URLs or logs contain tokens, the scanner’s checks around input validation and data exposure can identify risky patterns. Because middleBrick tests the unauthenticated attack surface, it can surface leakage without requiring credentials, providing a view of how an attacker might discover or harvest tokens.

When integrating identity via JWTs in Fiber, it is important to align with secure patterns such as storing tokens in HttpOnly, Secure cookies and avoiding any inclusion of tokens in logs or responses. middleBrick’s OpenAPI/Swagger analysis can further cross-reference spec definitions with runtime behavior to highlight mismatches, such as an endpoint documented as secure but returning sensitive token material. This supports compliance mappings to frameworks like OWASP API Top 10 and helps prioritize fixes based on risk scores provided by the scanner.

To remediate token leakage when using JWT tokens in Fiber, adopt secure coding and configuration practices that minimize exposure and enforce strict handling of tokens. Below are concrete code examples and configurations for a Fiber service.

1. Use HttpOnly, Secure cookies to store JWTs instead of sending them in response bodies or query parameters.

// Good: Set JWT in a secure cookie
package main

import (
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/session"
	"github.com/gofiber/fiber/v2/middleware/cors"
)

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

	// Secure CORS configuration
	app.Use(cors.New(cors.Config{
		AllowOrigins: "https://your-frontend.com",
		AllowCredentials: true,
	}))

	// Session middleware for secure cookie storage
	store := session.NewMemoryStore()
	app.Use(session.New(session.Config{
		Store:       store,
		Key:         "session_id",
		CookieHTTPOnly: true,
		CookieSecure:   true,  // only sent over HTTPS
		CookieSameSite: "lax",
	}))

	app.Post("/login", func(c *fiber.Ctx) error {
		// After validating credentials
		token := "your.jwt.token"
		// Store token in session cookie
		if err := c.Session().Set("token", token); err != nil {
			return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "login failed"})
		}
		// Do NOT return the token in the response body
		return c.JSON(fiber.Map{"message": "login successful"})
	})

	app.Listen(":3000")
}

2. Avoid logging or exposing JWTs in error messages and ensure validation errors do not echo tokens.

// Bad: Logging the Authorization header can leak tokens
// Good: Redact sensitive headers in logs
func safeHandler(c *fiber.Ctx) error {
	token := c.Get("Authorization")
	// Do not log the full header value
	c.Locals("request_id", "12345")
	// Process token without exposing it
	if token == "" {
		return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "authorization header missing"})
	}
	// Validate token and handle errors generically
	return c.JSON(fiber.Map{"data": "ok"})
}

3. Use short-lived tokens and secure refresh flows without exposing tokens in URLs.

// Do not pass tokens in query parameters
// Instead, use cookies or Authorization header: Bearer 
// Example of safe Authorization header usage
func authHeaderMiddleware(c *fiber.Ctx) error {
	auth := c.Get("Authorization")
	if len(auth) < 7 || auth[:7] != "Bearer " {
		return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid authorization format"})
	}
	// Extract and validate token without logging the raw value
	return c.Next()
}

4. Configure secure cookie attributes and avoid storing JWTs in localStorage where accessible to JavaScript.

By following these patterns, the risk of token leakage is reduced. middleBrick can validate these configurations by scanning endpoints and checking for insecure practices such as tokens in responses or missing Secure/HttpOnly flags. The CLI tool allows you to run scans from the terminal with middlebrick scan <url> and integrate checks into CI/CD using the GitHub Action to fail builds if security scores drop below your chosen threshold. For continuous monitoring, the Pro plan supports scheduled scans and alerts, while the MCP Server enables scanning APIs directly from AI coding assistants within your IDE.