Password Spraying in Echo Go with Basic Auth

Password spraying is an authentication technique where an attacker uses a small number of common passwords against many accounts, rather than credential stuffing (one credential per account). When an API built with Echo Go exposes a login endpoint that uses HTTP Basic Auth without additional protections, this pattern becomes both practical and high-risk.

In Echo Go, a typical Basic Auth handler might parse the Authorization header, split the base64-encoded credentials, and compare the username and password against a user store. If the endpoint simply returns 200 for a valid username/password pair and 401 for anything else—or, worse, uses a timing-sensitive string comparison—an attacker can iterate over a list of common passwords for a single user or across many users while observing only generic error messages. Because the scan is unauthenticated, middleBrick’s authentication checks will flag the presence of Basic Auth–protected routes and note whether timing differences allow account enumeration.

The combination of Basic Auth and password spraying is dangerous for several reasons. First, Basic Auth sends credentials in base64 on every request (easily decoded if intercepted), so spraying attempts are straightforward to perform and to observe via network traces. Second, Echo Go applications that do not enforce rate limiting on the login route allow rapid, low-volume requests that stay under typical per-IP thresholds, making detection harder. Third, if the handler leaks whether a username exists (different response codes or timing for valid vs invalid users), attackers can enumerate valid accounts before spraying passwords, compounding the risk. MiddleBrick’s checks for BOLA/IDOR, Authentication, and Rate Limiting are designed to surface these issues by correlating runtime behavior with the OpenAPI specification and identifying unauthenticated attack paths.

Consider an Echo Go route like the following, which accepts Basic Auth and performs a simple check:

func basicAuthMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		auth := c.Request().Header.Get("Authorization")
		if auth == "" {
			return c.NoContent(http.StatusUnauthorized)
		}
		const prefix = "Basic "
		if !strings.HasPrefix(auth, prefix) {
			return c.NoContent(http.StatusUnauthorized)
		}
		payload, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
		if err != nil {
			return c.NoContent(http.StatusUnauthorized)
		}
		creds := strings.SplitN(string(payload), ":", 2)
		if len(creds) != 2 {
			return c.NoContent(http.StatusUnauthorized)
		}
		username, password := creds[0], creds[1]
		if checkPassword(username, password) {
			return next(c)
		}
		return c.NoContent(http.StatusUnauthorized)
	}
}

If checkPassword returns a subtle timing difference or the HTTP handler returns different status codes depending on whether the username exists, an attacker running a password-spraying campaign can infer information incrementally. MiddleBrick’s parallel security checks, including Authentication and Rate Limiting, help identify whether such leakage or insufficient throttling exists without requiring credentials.

To reduce the risk of password spraying when using Basic Auth in Echo Go, apply a combination of constant-time comparison, generic error responses, and strict rate controls. The goal is to ensure that for any request to the authentication route, the server behaves the same regardless of whether the username is valid.

First, use a constant-time comparison for credentials to prevent timing-based account enumeration. Replace naive string equality with a function like subtle.ConstantTimeCompare from Go’s crypto/subtle package. Second, enforce rate limiting at the route level so that repeated requests from a single source are throttled. Third, return a uniform 401 response without indicating whether the username exists.

Here is a more secure version of the Basic Auth handler in Echo Go:

import (
	"crypto/subtle"
	"encoding/base64"
	"net/http"
	"strings"

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

// Simulated user store; in production, use a secure, salted hash comparison.
var userStore = map[string][]byte{
	"alice": []byte("correct horse battery staple"),
}

func secureCheckPassword(username, password string) bool {
	expected, ok := userStore[username]
	if !ok {
		// Use a dummy hash to keep timing consistent
		expected = []byte("dummy")
	}
	return subtle.ConstantTimeCompare([]byte(password), expected) == 1
}

func secureBasicAuthMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		auth := c.Request().Header.Get("Authorization")
		if auth == "" {
			return c.NoContent(http.StatusUnauthorized)
		}
		const prefix = "Basic "
		if !strings.HasPrefix(auth, prefix) {
			return c.NoContent(http.StatusUnauthorized)
		}
		payload, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
		if err != nil {
			return c.NoContent(http.StatusUnauthorized)
		}
		creds := strings.SplitN(string(payload), ":", 2)
		if len(creds) != 2 {
			return c.NoContent(http.StatusUnauthorized)
		}
		username, password := creds[0], creds[1]
		if secureCheckPassword(username, password) {
			return next(c)
		}
		return c.NoContent(http.StatusUnauthorized)
	}
}

Additionally, apply rate limiting at the group or route level to mitigate rapid spraying attempts:

e := echo.New()
rateLimiter := middleware.RateLimiter(middleware.DefaultRateLimiterConfig)
e.Use(rateLimiter)

e.POST("/login", secureBasicAuthMiddleware(loginHandler))

By combining constant-time checks, uniform error handling, and rate limiting, you reduce the effectiveness of password spraying against Basic Auth endpoints in Echo Go. MiddleBrick’s scans can verify whether these mitigations are reflected in runtime behavior and in the published API specification.