Cache Poisoning in Buffalo

Cache poisoning in Buffalo applications typically occurs when HTTP responses are cached without proper validation of request parameters. The most common attack pattern involves manipulating cache keys to serve malicious content to other users.

In Buffalo applications, cache poisoning often exploits the default caching middleware. Consider this vulnerable pattern:

func HomeHandler(c buffalo.Context) error {
    userID := c.Session().Get("userID").(int)
    user := models.GetUserByID(userID)
    
    // Vulnerable: caching without proper key validation
    c.Cache().Set("user_profile_"+c.Param("id"), user, 300)
    
    return c.Render(200, r.JSON(user))
}

An attacker can manipulate the id parameter to poison the cache. For example, requesting /profile?id=1 then /profile?id=2 might cause the cache to serve user 1's data to user 2.

Buffalo's default cache middleware uses a simple key generation strategy that can be predictable. When combined with insufficient input validation, this creates cache poisoning opportunities:

// Predictable cache key generation
func generateCacheKey(r *http.Request) string {
    return r.URL.Path + "?" + r.URL.RawQuery
}

// Vulnerable: predictable keys allow cache key collisions
func UserProfileHandler(c buffalo.Context) error {
    id := c.Param("id")
    cacheKey := "user_" + id
    
    if cached, ok := c.Cache().Get(cacheKey); ok {
        return c.Render(200, r.JSON(cached))
    }
    
    user := models.FindUser(id)
    c.Cache().Set(cacheKey, user, 300)
    return c.Render(200, r.JSON(user))
}

The vulnerability here is that cache keys are derived directly from user input without sanitization. An attacker can craft requests with special characters or path traversal attempts that cause cache collisions.

Another Buffalo-specific pattern involves template caching. If template rendering depends on user-controlled data without proper escaping:

func RenderTemplateHandler(c buffalo.Context) error {
    data := map[string]interface{}{
        "title": c.Param("title"),
        "content": c.Param("content"),
    }
    
    // Vulnerable: template output cached with unescaped user data
    return c.Render(200, r.HTML("template.plush.html", data))
}

This can lead to cache poisoning where malicious content gets cached and served to other users.

Detecting cache poisoning in Buffalo applications requires examining both code patterns and runtime behavior. Start by analyzing your middleware stack:

// Check for vulnerable middleware usage
func CheckMiddlewareStack() {
    app := buffalo.New(buffalo.Options{})
    
    // Look for default cache middleware
    for _, m := range app.Middlewares() {
        if m.Name() == "cache" {
            // Examine cache configuration
            config := m.Config()
            // Check for predictable key generation
        }
    }
}

middleBrick's black-box scanning can detect cache poisoning vulnerabilities by testing for:

• Predictable cache key generation patterns
• Insufficient input validation before caching
• Cross-user data leakage through cached responses
• Template rendering vulnerabilities

Runtime detection involves monitoring cache behavior:

func MonitorCacheBehavior() {
    cache := buffalo.NewCache()
    
    // Track cache key collisions
    collisions := make(map[string]int)
    
    // Monitor for suspicious patterns
    for request := range requestStream {
        key := generateCacheKey(request)
        if collisions[key] > threshold {
            // Potential cache poisoning attempt detected
            log.Warning("High cache key collision rate")
        }
    }
}

middleBrick specifically tests Buffalo applications by:

• Scanning for unauthenticated endpoints that use caching
• Testing for cache key predictability by varying request parameters
• Checking for cross-user data exposure in cached responses
• Analyzing template rendering for cached output vulnerabilities

The scanner examines your OpenAPI spec (if available) to understand caching behavior and then actively tests these endpoints for poisoning vulnerabilities.

Buffalo provides several built-in mechanisms to prevent cache poisoning. The most effective approach combines input validation, secure cache key generation, and proper cache isolation.

First, implement strict input validation before caching:

func SecureUserProfileHandler(c buffalo.Context) error {
    id := c.Param("id")
    
    // Validate input before using in cache key
    if !isValidUserID(id) {
        return c.Error(400, errors.New("invalid user ID"))
    }
    
    cacheKey := "user_profile_secure_" + id
    
    if cached, ok := c.Cache().Get(cacheKey); ok {
        return c.Render(200, r.JSON(cached))
    }
    
    user := models.FindUser(id)
    c.Cache().Set(cacheKey, user, 300)
    return c.Render(200, r.JSON(user))
}

func isValidUserID(id string) bool {
    // Strict validation to prevent cache key manipulation
    if len(id) == 0 || len(id) > 20 {
        return false
    }
    for _, char := range id {
        if !unicode.IsDigit(char) {
            return false
        }
    }
    return true
}

Buffalo's cache middleware supports custom key generation. Implement a secure key strategy:

func SecureCacheKeyGenerator(r *http.Request) string {
    // Include user-specific data and request hash
    userID := extractUserID(r)
    hash := hashRequestParameters(r)
    
    return fmt.Sprintf("secure_cache_%s_%s", userID, hash)
}

func extractUserID(r *http.Request) string {
    // Extract from secure context, not query params
    auth := r.Context().Value("auth")
    if auth == nil {
        return "guest"
    }
    return auth.(string)
}

func hashRequestParameters(r *http.Request) string {
    h := sha256.New()
    h.Write([]byte(r.URL.Path))
    h.Write([]byte(r.URL.RawQuery))
    return hex.EncodeToString(h.Sum(nil))[:8]
}

For template rendering, use Buffalo's built-in escaping and avoid caching unescaped user content:

func SafeTemplateHandler(c buffalo.Context) error {
    data := map[string]interface{}{
        "title": html.EscapeString(c.Param("title")),
        "content": html.EscapeString(c.Param("content")),
    }
    
    // Only cache after proper escaping
    return c.Render(200, r.HTML("safe_template.plush.html", data))
}

middleBrick's GitHub Action can automatically scan your Buffalo application in CI/CD:

- name: Scan Buffalo API
  uses: middleBrick/middlebrick-action@v1
  with:
    url: http://localhost:3000
    fail-on-severity: high
    token: ${{ secrets.MIDDLEBRICK_TOKEN }}

This integration catches cache poisoning vulnerabilities before deployment, ensuring your Buffalo application remains secure.