Memory Leak in Echo Go with Hmac Signatures

A memory leak in an Echo Go service that uses Hmac Signatures typically arises when byte buffers, cryptographic contexts, or request-scoped objects are retained beyond their intended lifetime. In Go, memory is managed by garbage collection, but logical leaks still occur when references prevent eligible objects from being reclaimed. With Hmac Signatures, the leak often surfaces in the request lifecycle where the signature is computed, verified, or stored.

Consider a handler that reads a large request body into a byte slice to compute an Hmac, then passes that slice into a context for later use without cleaning up references. The context may keep the underlying byte array alive for the duration of the request and beyond, especially if the context is reused or if developers attach the full payload to the context for convenience. Similarly, if an Hmac verification function allocates buffers for intermediate states (e.g., hashing.Hash implementations) and those buffers are stored in long-lived caches or global variables, the garbage collector cannot free them, leading to steady memory growth under sustained load.

Echo Go routes are registered once and reused for every request; if a handler captures variables by reference and those references hold onto large payloads or cryptographic state, the objects remain reachable for the lifetime of the handler. This is common when developers bind the request body to a struct field or store computed signatures in a map keyed by request identifiers without eviction. Over time, the runtime heap grows, increasing GC pause frequency and overall memory footprint. Because the attack surface is unauthenticated, an attacker can trigger this pattern at scale by sending many requests with large bodies or crafted headers that influence signature processing, causing the service to consume more memory than expected.

In the context of middleBrick’s 12 security checks, a Memory Leak finding may be surfaced when scans detect abnormal resource retention during black-box testing of the unauthenticated endpoint. The scanner does not inspect internal code, but it can observe symptoms such as increasing response times or resource consumption patterns consistent with unbounded growth. Proper handling of Hmac Signatures in Echo Go requires ensuring that buffers are scoped tightly, contexts do not retain payloads, and cryptographic objects are not stored in long-lived caches without size limits or eviction policies.

Remediation focuses on limiting object lifetimes, avoiding unnecessary retention of request data, and ensuring cryptographic operations do not create long-lived references. Below are concrete patterns and code examples for Echo Go handlers using Hmac Signatures.

Example 1: Compute and verify Hmac without retaining the request body

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

	"github.com/labstack/echo/v4"
)

func verifyHmac(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		// Read a limited-size body stream for signature verification
		const maxBody = 1 << 20 // 1 MiB
		body := io.LimitReader(c.Request().Body, maxBody)
		defer c.Request().Body.Close()

		expectedSig := c.Request().Header.Get("X-API-Signature")
		if expectedSig == "" {
			return echo.NewHTTPError(http.StatusBadRequest, "missing signature")
		}

		mac := hmac.New(sha256.New, []byte("secret-key"))
		if _, err := io.Copy(mac, body); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, "invalid payload")
		}
		computed := mac.Sum(nil)

		// Use constant-time comparison to avoid timing leaks
		if !hmac.Equal(computed, []byte(expectedSig)) {
			return echo.NewHTTPError(http.StatusUnauthorized, "invalid signature")
		}

		// Proceed without attaching body or signature to context
		return next(c)
	}
}

This pattern avoids storing the body in a variable and ensures the reader is closed promptly. The Hmac is computed on a limited stream, and no references to the payload are kept beyond the verification step.

Example 2: Avoid context pollution with large objects

func handler(c echo.Context) error {
	// Do NOT do this:
	// type MyPayload struct { Data []byte `json:"data"` }
	// var p MyPayload
	// if err := c.Bind(&p); err != nil { ... }
	// c.Set("payload", p) // keeps large Data in context

	// Instead, process incrementally and store only what is necessary
	const maxBody = 1 << 20
	buf := make([]byte, maxBody)
	n, err := c.Request().Body.Read(buf)
	if err != nil && err != io.EOF {
		return echo.NewHTTPError(http.StatusBadRequest, "read error")
	}
	defer c.Request().Body.Close()

	// Compute Hmac on the slice and then zero it when done
	mac := hmac.New(sha256.New, []byte("secret-key"))
	mac.Write(buf[:n])
	sig := mac.Sum(nil)

	// Use sig for verification or signing downstream
	_ = sig

	// Explicitly release reference
	buf = nil

	return c.NoContent(http.StatusOK)
}

Here, the payload is read into a bounded buffer, used immediately, and then released. The buffer is set to nil to aid garbage collection. This prevents the handler from holding onto large objects via context or global caches.

Example 3: Do not store Hmac keys or intermediate hashes in long-lived maps

var (
	// Avoid caching computed Hmac results keyed by raw payload unless you enforce eviction
	// badCache = make(map[string][]byte)
)

func safeSign(key []byte, payload []byte) []byte {
	mac := hmac.New(sha256.New, key)
	mac.Write(payload)
	return mac.Sum(nil) // return a new slice; caller decides lifetime
}

By avoiding global or package-level caches for Hmac outputs, you ensure that cryptographic artifacts do not accumulate. If caching is required for performance, implement size-bounded structures with TTL or LRU eviction.