Cache Poisoning in Buffalo with Bearer Tokens

Cache poisoning occurs when an attacker causes a cache to store malicious content, leading other users to receive that content instead of the intended response. In the Buffalo framework, this can happen when responses are cached based on request path or headers without properly considering authorization tokens such as Bearer Tokens.

When a Buffalo application caches responses at the HTTP or application layer and uses Bearer Tokens for authentication, a failure to include the Authorization header in the cache key can cause the server to serve a cached response that was originally generated for an authenticated user to an unauthenticated or different user. For example, if a request with a valid Bearer Token retrieves user-specific data and the response is cached without the Authorization header as part of the key, subsequent requests without a token or with a different token may receive the cached sensitive data.

Consider a scenario where an endpoint /api/profile returns user-specific information and caches the response for performance. If the caching logic does not incorporate the Authorization header, an authenticated request with a Bearer Token might populate the cache. Later, an unauthenticated request to the same endpoint could receive the cached user data, leading to information disclosure. This becomes more critical when tokens are passed in the Authorization header as Bearer <token>, and the caching layer does not treat each token as a distinct cache entry.

Buffalo does not inherently cache responses, so caching is typically introduced via middleware or external systems such as reverse proxies or in-memory stores. If these systems use the request path alone to determine cache keys, they may inadvertently mix responses that should be segregated by authentication context. Attackers may exploit this by making authenticated requests to learn cached sensitive information or by manipulating cache behavior to poison stored responses.

To identify this risk during scanning, middleBrick checks whether responses that include authentication headers are being cached in a way that ignores those headers. This detection helps highlight configurations where token-based access controls are bypassed by caching mechanisms, exposing user-specific data across different security contexts.

To prevent cache poisoning when using Bearer Tokens in Buffalo, ensure that the cache key includes the Authorization header or a derived value such as the user identifier. Avoid caching sensitive responses for different authentication contexts under the same key.

Below are examples of how to handle Bearer Tokens securely in Buffalo and how to structure caching to avoid mixing user contexts.

Example 1: Skipping cache for authenticated requests

Configure your caching middleware to bypass the cache when an Authorization header is present.

// In your middleware or cache logic
func SkipCacheForAuth(h web.HandlerFunc) web.HandlerFunc {
    return func(c buffalo.Context) error {
        auth := c.Request().Header.Get("Authorization")
        if auth != "" && len(auth) > 7 && auth[:7] == "Bearer " {
            // Do not use cache for requests with Bearer Tokens
            return c.SkipMiddleware()
        }
        return h(c)
    }
}

app.GET("/api/profile", SkipCacheForAuth(func(c buffalo.Context) error {
    userID := c.CurrentUser.ID
    var profile UserProfile
    if err := db.Where("user_id = ?", userID).First(&profile); err != nil {
        return c.Error(500, err)
    }
    return c.Render(200, r.JSON(profile))
}))

Example 2: Including user ID in cache key

If caching is required for authenticated endpoints, incorporate the user ID or a token-derived identifier into the cache key.

func UserProfileHandler(c buffalo.Context) error {
    auth := c.Request().Header.Get("Authorization")
    var userID string
    if auth != "" && len(auth) > 7 && auth[:7] == "Bearer " {
        token := auth[7:]
        // Validate token and extract user ID (pseudo-code)
        userID, _ = extractUserIDFromToken(token)
    }
    cacheKey := fmt.Sprintf("user_profile_%s", userID)
    var profile UserProfile
    if err := cache.Get(cacheKey, &profile); err != nil {
        // Fetch from database
        db.Where("id = ?", userID).First(&profile)
        cache.Set(cacheKey, profile, 5*time.Minute)
    }
    return c.Render(200, r.JSON(profile))
}

Example 3: Using request-based cache keys in a reverse proxy

When using a reverse proxy or CDN, ensure that cache keys include the Authorization header or that authenticated routes are excluded from caching.

# Example configuration for a proxy (not Buffalo code)
# Do not cache responses with Authorization headers
CacheKey "{req.url}" {req.headers.Authorization ? "private" : "default"}

These practices reduce the risk of cached data being shared across users with different authentication states. middleBrick can detect whether responses with Bearer Tokens are improperly cached and provide guidance to align your implementation with secure caching patterns.