Cache Poisoning in Echo Go with Basic Auth

Cache poisoning occurs when an attacker manipulates a cache key so that malicious or incorrect data is served to other users. In Echo Go, when Basic Auth is used without additional safeguards, the HTTP request’s Authorization header can become part of the cache key if the caching layer or reverse proxy does not strip it. This means responses authenticated for one user may be cached and later served to another user with different credentials, effectively leaking one user’s data to another.

Echo Go does not provide built-in caching, so caching is typically implemented at the infrastructure level (e.g., CDN, reverse proxy, or in-memory cache). When Basic Auth credentials are transmitted in the Authorization header on every request, a caching system that uses the full request—including headers—as the cache key will store separate entries per user. However, if the cache key is derived from the request URI only and the Authorization header is mistakenly included in the key or not excluded, authenticated responses can be incorrectly shared across users. This is especially risky when the cache is shared across roles with different permissions, such as an administrative endpoint cached alongside a public endpoint using the same URI path but different Authorization values.

An attacker who can cause a request with a privileged Authorization header to be cached (e.g., by inducing a logged-in admin to visit a crafted URL) may then force unauthenticated or lower-privileged users to receive the cached privileged response. Because Basic Auth sends credentials on every request, the cache may treat each authenticated session as unique, but misconfigured shared caches can collapse these into a single entry, leading to horizontal or vertical privilege escalation through cached content. This violates the principle of authorization separation and can expose sensitive data or functionality to unintended clients.

For example, consider an endpoint /api/v1/users that returns user-specific data. If an admin’s request with a valid Basic Auth header is cached under a key that does not exclude the Authorization header, a subsequent request from a standard user to the same URI might receive the admin’s cached data. The Echo Go application may assume the data is correct for the requesting user, but the cache returns another user’s information due to key collision. This scenario maps to the BOLA/IDOR category and can be detected by middleBrick during its parallel security checks, which include Authorization testing and Inventory Management to ensure endpoints respect scope and permissions.

middleBrick scans such endpoints without authentication by default, testing the unauthenticated attack surface to identify whether caching behavior leaks data across users or roles. Its LLM/AI Security checks also probe for indirect exposures that could arise from mishandled responses. Findings include severity-ranked results and remediation guidance, helping teams recognize that caching and authentication must be explicitly coordinated in Go applications.

To mitigate cache poisoning when using Basic Auth in Echo Go, ensure that cached responses are segregated by user or role, and that caching infrastructure excludes the Authorization header from cache keys for endpoints where user context affects the response. The following patterns demonstrate secure handling.

1. Avoid caching authenticated responses at the infrastructure layer

Configure your cache or reverse proxy to not cache responses when the Authorization header is present, or to strip the header before using it as a cache key. In an Nginx or CDN context, set rules to bypass caching for requests containing Authorization. In Go middleware, you can also skip caching for authenticated routes.

// Example: Echo middleware that disables caching for authenticated requests
package main

import (
	"net/http"
	"github.com/labstack/echo/v4"
)

func NoCacheMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		// If Authorization header is present, ensure cache-control headers prevent caching
		if c.Request().Header.Get("Authorization") != "" {
			c.Response().Header().Set("Cache-Control", "no-store, no-cache, must-revalidate, max-age=0")
			c.Response().Header().Set("Pragma", "no-cache")
			c.Response().Header().Set("Expires", "0")
		}
		return next(c)
	}
}

func main() {
	e := echo.New()
	e.Use(NoCacheMiddleware)

	e.GET("/api/v1/users", func(c echo.Context) error {
		// Handler logic here
		return c.JSON(http.StatusOK, map[string]string{"message": "user-specific data"})
	})

	e.Start(":8080")
}

2. Use role-based or user-based cache keys when caching is required

If you must cache authenticated responses, derive cache keys from both the request URI and a normalized user or role identifier, and never share cache entries across different Authorization contexts. This prevents one user’s data from being served to another.

// Example: Generating a cache key that includes user ID extracted from Basic Auth
package main

import (
	"fmt"
	"net/http"
	"strings"

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

func extractUserIDFromBasicAuth(auth string) (string, bool) {
	// In practice, validate and decode credentials securely
	if auth == "" || !strings.HasPrefix(auth, "Basic ") {
		return "", false
	}
	// Decode base64 payload and extract username as a simple user identifier
	// This is illustrative; use proper credential validation in production
	split := strings.SplitN(auth, " ", 2)
	if len(split) != 2 {
		return "", false
	}
	// Assume decoded payload is "username:password"
	payload := split[1]
	// In real code, decode base64
	parts := strings.Split(payload, ":")
	if len(parts) < 1 {
		return "", false
	}
	return parts[0], true
}

func CacheKeyMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		auth := c.Request().Header.Get("Authorization")
		userID := "anonymous"
		if auth != "" {
			if id, ok := extractUserIDFromBasicAuth(auth); ok {
				userID = id
			}
		}
		// Store userID in context for cache key construction downstream
		c.Set("cacheKeySuffix", userID)
		return next(c)
	}
}

func main() {
	e := echo.New()
	e.Use(CacheKeyMiddleware)

	e.GET("/api/data", func(c echo.Context) error {
		// Use c.Get("cacheKeySuffix") when interacting with your cache layer
		return c.JSON(http.StatusOK, map[string]string{"data": "cached per user"})
	})

	e.Logger.Fatal(e.Start(":8080"))
}

3. Validate credentials and scope before using cached data

Ensure that cached responses are only reused when the requesting user’s permissions align with the cached data’s scope. Do not serve admin-level cached responses to users lacking admin privileges, even if the cache key appears similar.

These steps reduce the risk of cache poisoning by ensuring that Authorization context is considered in caching decisions. middleBrick’s continuous monitoring and OWASP API Top 10 mappings can help verify that such controls are effective in practice.