Memory Leak in Fiber with Hmac Signatures

A memory leak in a Fiber application that uses Hmac Signatures typically arises when request context or cryptographic state is retained beyond the request lifecycle. In Go, memory that remains referenced is not garbage collected. When you compute an Hmac signature per request and store references to request-specific data (such as the request body, parsed headers, or a mutable context map) in long-lived structures, the associated memory cannot be freed until those structures are explicitly released or the structure itself is garbage collected.

For example, attaching a per-request Hmac signature to a global cache or a reused context object without cleaning up entries after the request completes can cause unbounded growth. This pattern is common when developers use middleware to compute and store signatures for replay protection or audit logging but forget to evict or limit the stored data. Over time, the process heap grows, increasing latency and potentially leading to out-of-memory conditions under sustained load.

Another scenario involves improper handling of buffers used during signature computation. If a buffer is allocated per request (e.g., via make([]byte, size)) and referenced by a closure or a global structure after the handler returns, the garbage collector cannot reclaim it. Fiber’s performance-oriented design encourages reuse of objects; without careful scoping, this can inadvertently keep large buffers alive.

When combined with OpenAPI/Swagger analysis, such runtime leaks may not be evident from static spec definitions. The scanner’s runtime checks can surface unusual memory patterns correlated with Hmac processing, helping to identify endpoints where signature logic interacts poorly with request context management.

These issues fall under the broader checks performed by middleBrick’s 12 security checks, including Input Validation and Unsafe Consumption, where unexpected data handling patterns can exacerbate resource retention. middleBrick detects anomalies and provides findings with remediation guidance, though it does not fix or block the underlying condition.

To prevent memory leaks when using Hmac Signatures in Fiber, ensure that per-request cryptographic state does not escape the request handler scope. Use local variables and avoid attaching computed signatures or related buffers to global or long-lived objects. Below are concrete, working code examples for safe Hmac handling in Fiber.

Example 1: Compute and verify Hmac within the request handler without retaining state

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"fmt"
	"net/http"

	"github.com/gofiber/fiber/v2"
)

func main() {
	app := fiber.New()
	secret := []byte("super-secret-key")

	app.Post("/webhook", func(c *fiber.Ctx) error {
		// Read body once; avoid retaining the raw body in global caches
		payload := c.Body()

		// Compute Hmac signature for verification
		mac := hmac.New(sha256.New, secret)
		mac.Write(payload)
		expectedMAC := mac.Sum(nil)

		// Retrieve client signature from header
		clientSig := c.Get("X-Signature")
		if !hmac.Equal(expectedMAC, []byte(clientSig)) {
			return c.Status(http.StatusUnauthorized).SendString("invalid signature")
		}

		// Process request without storing signature or payload beyond this scope
		return c.SendString("ok")
	})

	app.Listen(":3000")
}

Example 2: Use request-scoped context values carefully; avoid global maps

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"fmt"
	"net/http"

	"github.com/gofiber/fiber/v2"
)

func main() {
	app := fiber.New()
	secret := []byte("super-secret-key")

	// Avoid: var cache = map[string][]byte{} // global cache can cause leaks

	app.Get("/data", func(c *fiber.Ctx) error {
		// Compute signature locally; do not assign to a global or reused context map
		h := hmac.New(sha256.New, secret)
		h.Write([]byte(c.Params("id")))
		sig := h.Sum(nil)

		// Use signature for verification or temporary processing only
		if !hmac.Equal(sig, []byte(c.Get("X-Requested-With"))) {
			return c.Status(http.StatusForbidden).SendString("forbidden")
		}

		// Ensure no references to sig or intermediate buffers escape this function
		return c.JSON(fiber.Map{"id": c.Params("id"), "valid": true})
	})

	app.Listen(":3000")
}

Best practices summary

• Keep cryptographic buffers and signatures local to the handler; do not store them in globals or long-lived maps.
• Reuse objects intentionally with controlled lifetimes; avoid implicit retention via closures that capture request-specific data.
• If you must cache, implement size limits and TTL-based eviction to prevent unbounded memory growth.

These remediation steps align with secure coding practices for Hmac usage and help mitigate memory retention issues that could be flagged during middleBrick’s runtime scans.