Cache Poisoning in Echo Go with Dynamodb

Cache poisoning in the combination of Echo Go and DynamoDB typically arises when an application uses unvalidated or unkeyed data to construct cache keys, or when it reflects user-controlled input into cache identifiers and downstream DynamoDB queries. If an attacker can influence the cache key, they may cause the application to store and serve malicious or incorrect responses from cache, or force repeated cache misses that trigger unintended DynamoDB request patterns.

Specifically in Echo Go, route parameters, query strings, and headers are often used directly to form cache keys. If these values are concatenated into a cache key without normalization, canonicalization, or strict allow-listing, an attacker can manipulate the key to collide with other users’ data or to trigger specific DynamoDB partition key requests. For example, a key built as userID + ":profile" becomes vulnerable if userID is attacker-controlled and not validated, enabling horizontal privilege escalation through cache key manipulation.

DynamoDB amplifies the impact when the poisoned cache key leads to repeated queries with crafted partition key values. If the application uses the cache to avoid repeated DynamoDB calls, an attacker who forces cache misses may cause excessive read activity on specific partitions, contributing to noisy patterns that can be correlated with reconnaissance or potential DoSS-style effects under provisioned capacity. Additionally, if the application caches sensitive query responses keyed by user input without integrity checks, tampered cache entries can persist and be served to other users, exposing data across tenant boundaries.

Another angle involves response caching when the application caches DynamoDB query results and later reuses them in a different security context. For instance, if a cached item for one user is mistakenly keyed in a way that allows another user’s request to match the same cache key, the second user may receive the first user’s data. This is a form of cache poisoning that violates isolation boundaries. MiddleBrick detects these risks under its Property Authorization and BOLA/IDOR checks, highlighting how unvalidated inputs and weak cache-key design can expose DynamoDB-backed services in Echo Go applications.

To remediate cache poisoning risks in Echo Go with DynamoDB, focus on strict cache-key construction, input validation, and isolation guarantees. Always derive cache keys from a canonical representation of the request context and avoid direct concatenation of user input. Use cryptographic hashes (e.g., SHA-256) over normalized inputs to produce stable, non-guessable keys, and scope keys with tenant or user identifiers that are verified server-side.

Validate and sanitize all inputs that influence DynamoDB queries and cache behavior. Use allow-lists for known-safe values for parameters that affect partition key or sort key construction, and enforce strict type and format checks before using them in cache logic. Ensure that cache entries are tagged or namespaced with tenant identifiers and that retrieval logic verifies ownership before returning cached content.

Example of safe DynamoDB interaction in Go using the AWS SDK for Go v2, with explicit key construction and no direct reflection of raw user input into cache keys:

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"

	dynamodb "github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

// buildCacheKey creates a deterministic, non-user-controlled cache key
func buildCacheKey(userID, scope string) string {
	h := sha256.New()
	h.Write([]byte(fmt.Sprintf("user:%s:scope:%s", userID, scope)))
	return hex.EncodeToString(h.Sum(nil))
}

// GetUserProfile retrieves profile data safely with canonical cache key
func GetUserProfile(ctx context.Context, db *dynamodb.Client, userID, scope string) (map[string]interface{}, error) {
	// Validate userID format before use
	if !isValidUserID(userID) {
		return nil, fmt.Errorf("invalid user identifier")
	}
	cacheKey := buildCacheKey(userID, scope)
	// pseudo-code: cache retrieval using cacheKey
	// item, found := cache.Get(cacheKey)
	// if found { return item, nil }

	// Fallback to DynamoDB with parameterized key
	key := map[string]interface{}{
		"user_id": &dynamodb.AttributeValueMemberS{Value: userID},
	}
	out, err := db.GetItem(ctx, &dynamodb.GetItemInput{
		TableName: aws.String("UserProfiles"),
		Key:       key,
	})
	if err != nil {
		return nil, err
	}
	// On cache hit, store using cacheKey to avoid future repeated lookups
	// cache.Set(cacheKey, out.Item, ttl)
	return out.Item, nil
}

func isValidUserID(id string) bool {
	// Allow only alphanumeric and underscores, non-empty, bounded length
	// Example regex validation can be applied here
	return len(id) > 0 && len(id) <= 64
}

When integrating with Echo Go, ensure that route parameters and query values are validated before being used in DynamoDB key expressions or cache logic:
import (
	"net/http"
	"strings"

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

func ProfileHandler(c echo.Context) error {
	userID := strings.TrimSpace(c.Param("userID"))
	if !isValidUserID(userID) {
		return echo.NewHTTPError(http.StatusBadRequest, "invalid user identifier")
	}
	// Proceed with safe DynamoDB and cache usage as shown above
	return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
}