Cache Poisoning in Echo Go (Go)

Cache poisoning in an Echo Go service occurs when an attacker influences cached responses so that malicious content is served to subsequent users. In Go applications using the echo framework, this risk arises when response caching depends on attacker-controlled inputs such as query parameters, headers, or path segments without proper validation or normalization.

Consider an endpoint that caches user profile data by concatenating a user-supplied Accept-Language header with the response key. If the header is reflected into the cache key without validation, an attacker can craft requests with crafted header values that cause distinct poisoned entries. Because Echo Go routes and middleware are highly configurable, developers might inadvertently use request attributes directly in cache logic, expanding the attack surface. The unauthenticated scan capabilities of middleBrick can surface such input validation and data exposure findings, highlighting where cache-related inputs are not sufficiently constrained.

Real-world cache poisoning often intersects with other OWASP API Top 10 risks like Improper Inventory Management and Unsafe Consumption, especially when APIs rely on external caches or shared infrastructure. For example, if an Echo Go service uses a shared CDN or in-memory cache without isolating tenant-specific data, an attacker who can poison one tenant’s entry may affect others. The risk is compounded when responses include sensitive data or when cache keys do not incorporate tenant context. middleBrick’s checks for input validation and data exposure help identify missing isolation and improper cache segregation, which are critical for preventing poisoned cache entries from being served across different users or sessions.

Additionally, misconfigured caching behavior can be chained with other issues such as IDOR or BOLA to amplify impact. If an API caches per identifier without verifying access rights, a poisoned cache entry might persist across privilege changes, causing incorrect data to be delivered long after the initial injection. Because Echo Go encourages composable middleware stacks, developers must ensure that any caching layer explicitly incorporates authorization context and validates all inputs that participate in cache key construction.

To remediate cache poisoning in Echo Go, ensure that cache keys are deterministic, normalized, and scoped to include tenant or user context. Avoid using raw, attacker-controlled inputs directly in cache keys. Instead, sanitize and validate inputs, and incorporate authorization context so that cached responses cannot be shared across unauthorized users or tenants.

The following example demonstrates a secure approach for an Echo Go handler that caches user profile responses. It uses a normalized cache key that includes the authenticated user ID and a validated language tag, avoiding direct use of request headers.

//go
package main

import (
	"context"
	"net/http"
	"strings"

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

// sanitizeLanguage ensures the language tag is safe for use in a cache key.
// It allows only alphanumeric and hyphen, and limits length.
func sanitizeLanguage(lang string) string {
	var b strings.Builder
	for _, r := range lang {
		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '-' || r == '_' {
			b.WriteRune(r)
		}
	}
	out := b.String()
	if out == "" {
		return "en" // default safe fallback
	}
	// limit length to avoid excessively large keys
	if len(out) > 10 {
		out = out[:10]
	}
	return out
}

// ProfileResponse represents a cached user profile.
type ProfileResponse struct {
	Username string `json:"username"`
	Bio      string `json:"bio"`
}

// GetUserProfile is an Echo handler with cache-aware controls.
func GetUserProfile(c echo.Context) error {
	user := c.Get("user") // assume authenticated user set by prior middleware
	userID, ok := user.(string)
	if !ok || userID == "" {
		return echo.NewHTTPError(http.StatusUnauthorized, "invalid user context")
	}

	req := c.Request()
	lang := req.Header.Get("Accept-Language")
	lang = sanitizeLanguage(lang)

	cacheKey := "profile:user: " + userID + ":lang=" + lang
	// Here you would use your caching client (e.g., Redis, in-memory) to Get/Set.
	// Example pseudo-code:
	// if val, found := cache.Get(cacheKey); found { return c.JSONBlob(val) }
	// data := fetchProfile(userID, lang)
	// cache.Set(cacheKey, data, ttl)
	// return c.JSONBytes(data)

	// Placeholder response for demonstration.
	resp := ProfileResponse{
		Username: userID,
		Bio:      "Sample bio for " + userID,
	}
	return c.JSON(http.StatusOK, resp)
}

Additional remediation practices include:

• Isolate cache entries by tenant or namespace, incorporating tenant ID into the cache key.
• Validate and normalize all inputs that influence caching behavior, including query parameters, headers, and cookies.
• Avoid caching sensitive or user-specific responses in shared caches unless strict isolation is guaranteed.
• Use middleware to enforce authentication and authorization before cache lookup so that cached responses respect access controls.
• Set appropriate TTLs and consider cache-invalidation strategies to limit the window of impact for any poisoned entry.

By combining input validation, tenant-aware scoping, and disciplined cache key design, Echo Go services can mitigate cache poisoning risks while maintaining performance and correctness.