Cache Poisoning in Buffalo (Go)

Cache poisoning in a Buffalo application with Go occurs when an attacker manipulates cache keys or cache entries so that malicious or incorrect data is served to users. Buffalo applications often use server-side or in-memory caching for performance, and if cache identifiers are derived from uncontrolled inputs, an attacker can cause cache key collisions or overwrite legitimate cached responses.

Buffalo encourages developers to use helpers and context values to build response keys. If these keys incorporate user-supplied data such as query parameters, headers, or path segments without normalization or strict validation, an attacker can craft requests that map to the same cache entry as another user, leading to data leakage or incorrect content being cached and returned. For example, a cached user profile endpoint that includes the user ID in the cache key may inadvertently share entries if IDs are not properly scoped or namespaced.

The Go HTTP stack used by Buffalo does not inherently sanitize inputs before they participate in cache logic. Developers must ensure that cache keys are deterministic, scoped by tenant or session where appropriate, and that sensitive data is never stored in shared caches. A realistic scenario: an endpoint /products?category=electronics caches responses using a key built from the raw query string. An attacker can inject a poisoned query parameter that causes the application to cache a response containing other users’ data or malicious content, and subsequent requests for different categories may receive the poisoned response.

Because Buffalo applications are typically built with Go’s strong typing, the risk can be compounded when cache keys are constructed using string concatenation without canonicalization. For instance, mixing JSON representations, URL-encoded values, or custom delimiters can produce keys that appear distinct but collide under certain inputs, enabling an attacker to overwrite or read cached entries. This is especially dangerous when the cache is shared across users or when time-based eviction is used without proper isolation.

middleBrick scans APIs and web applications for cache poisoning risks by analyzing input handling, caching logic, and response variability. It flags endpoints that use unvalidated inputs in cache-related behavior and provides remediation guidance tailored to frameworks such as Buffalo in Go.

To mitigate cache poisoning in Buffalo applications written in Go, ensure cache keys are deterministic, scoped, and isolated. Use a structured approach to key construction that excludes user-controlled or variable parts that an attacker can manipulate. Below are concrete code examples demonstrating safe practices.

1. Normalize and scope cache keys

Do not directly concatenate raw query parameters into cache keys. Instead, parse, validate, and normalize inputs before use.

// Safe cache key construction in Buffalo
func buildCacheKey(c buffalo.Context, base string) string {
    // Assume userID is validated and extracted from session
    userID, _ := session.GetInt(c, "user_id")
    // Normalize query parameters
    category := c.Params().Get("category")
    if category == "" {
        category = "default"
    }
    // Use a deterministic, scoped key
    return fmt.Sprintf("cache:%s:user:%d:category:%s", base, userID, strings.ToLower(strings.TrimSpace(category)))
}

func ProductsHandler(c buffalo.Context) error {
    key := buildCacheKey(c, "products")
    var products []Product
    if found := cache.Get(key, &products); !found {
        // Fetch from database
        products = fetchProducts(c)
        cache.Set(key, products, 5*time.Minute)
    }
    return c.Render(200, r.JSON(products))
}

2. Isolate cache entries by tenant or session

When serving multiple users or organizations, include tenant or session identifiers in the cache key to prevent cross-user contamination.

// Scoped cache key with tenant isolation
func scopedCacheKey(c buffalo.Context, scope string) string {
    tenantID, _ := c.Value("tenant_id").(string)
    if tenantID == "" {
        tenantID = "public"
    }
    return fmt.Sprintf("tenant:%s:%s", tenantID, scope)
}

func ReportHandler(c buffalo.Context) error {
    key := scopedCacheKey(c, "daily_report")
    var data ReportData
    if cache.Get(key, &data) {
        return c.Render(200, r.JSON(data))
    }
    // Generate report
    data = generateReport(c)
    cache.Set(key, data, time.Hour)
    return c.Render(200, r.JSON(data))
}

3. Avoid caching sensitive or user-specific responses

Do not cache responses that contain private data unless the cache key fully isolates the data to the requesting user and the data is not considered sensitive across users.

// Example: do not cache user-specific data in shared cache
func MeHandler(c buffalo.Context) error {
    userID, _ := currentUser(c).ID()
    key := fmt.Sprintf("user:profile:%d", userID)
    var profile Profile
    if cache.Get(key, &profile) {
        return c.Render(200, r.JSON(profile))
    }
    profile = loadProfile(userID)
    // Use a per-user cache with strict access controls
    cache.Set(key, profile, 10*time.Minute)
    return c.Render(200, r.JSON(profile))
}

These practices align with remediation guidance available in security tools that test API endpoints for cache poisoning, such as middleBrick, which can identify risky caching patterns in Buffalo applications and provide prioritized findings with severity and fix directions.