Cache Poisoning in Buffalo with Api Keys

Cache poisoning in the Buffalo web framework occurs when an attacker can cause the application to store and serve malicious responses from its cache. When Api Keys are involved, the risk pattern changes: keys intended for authentication or rate limiting may be inadvertently incorporated into cache keys, causing sensitive or user-specific responses to be shared across users. If a route uses the Api Key header as part of the cache key but does not segregate responses by authorization context, one user’s cached data may be served to another user, leaking information or enabling privilege escalation.

Consider a Buffalo app that caches GET responses keyed by the request path and the Api Key value. An attacker who can obtain or guess a victim’s Api Key could poison the shared cache by requesting a crafted URL that causes the server to cache a response containing the victim’s data. Because the cache key includes the Api Key, other requests with the same key receive the poisoned response, potentially exposing personal or sensitive information. This violates confidentiality and can bypass authorization assumptions, especially when the cache is shared or reverse-proxy based. Common contributing factors include missing Vary headers, unsafe use of request headers in cache logic, and storing responses that should be user-specific without proper isolation.

For example, an endpoint like /api/users/me that uses an Api Key header to identify the client might cache a JSON user profile using a key derived from the header. If the cache key does not exclude roles or authorization context, an attacker who knows another user’s Api Key could retrieve that user’s cached profile. In a Buffalo application, this typically indicates that caching logic does not account for authorization boundaries. The scanner checks related to Authentication and BOLA/IDOR help surface such unsafe caching behaviors by correlating authenticated routes with cache-related headers and response variability.

To mitigate cache poisoning when using Api Keys in Buffalo, ensure that cached responses are segregated by authorization context and that sensitive headers are excluded from cache keys. Avoid including Api Keys directly in cache keys; instead, use stable identifiers that do not carry secrecy. Below are concrete code examples demonstrating safe caching patterns in a Buffalo application.

Example 1: Safe caching without Api Key in the cache key

Use a stable route-based cache key and exclude sensitive headers. Configure caching in actions/app.go or a before/after wrapper, and do not rely on Api Key values for cache discrimination.

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo/middleware"
)

func app() *buffalo.App {
    app := buffalo.New(buffalo.Options{
        Env:         ENV,
        SessionStore: &middleware.SessionCookieStore{},
    })

    // Use a fixed cache key per route and vary by Accept and Authorization scope, not the raw key
    app.GET("/api/users/me", func(c buffalo.Context) error {
        // Extract user identity from validated context (e.g., after auth middleware)
        userID := c.Value("current_user_id") // set by auth middleware, not from header at cache time
        cacheKey := "v1:users:me:" + userID.String()

        var profile UserProfile
        found := cache.Get(cacheKey, &profile)
        if !found {
            // Build profile from database using the authenticated user context
            profile = fetchUserProfile(c)
            cache.Set(cacheKey, profile, ttl)
        }
        return c.Render(200, r.JSON(profile))
    })
    return app
}

Example 2: Using Vary headers and excluding keys from shared caches

Ensure responses include appropriate Vary headers when authorization or headers are considered. Avoid caching user-specific responses in shared caches unless keys are anonymized.

import (
    "net/http"
    "github.com/gobuffalo/buffalo"
)

func apiKeySafeMiddleware(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        // Do not use raw Api Key in cache logic; validate and map to a user context
        apiKey := c.Request().Header.Get("X-API-Key")
        userID, err := validateApiKeyAndExtractUserID(apiKey)
        if err != nil {
            return c.Error(401, errors.New("unauthorized"))
        }
        c.Set("current_user_id", userID)

        // Suggest Vary on Authorization scope if caching at a shared layer
        c.Response().Header().Set("Vary", "Authorization")
        return next(c)
    }
}

func fetchUserProfile(c buffalo.Context) UserProfile {
    userID := c.Value("current_user_id")
    var profile UserProfile
    // DB query using userID from context
    return profile
}

Best practices summary

• Do not include raw Api Key values in cache keys; use mapped user or role identifiers instead.
• Set Vary headers appropriately to prevent shared caches from serving mismatched responses.
• Isolate user-specific cache entries by authenticated user ID rather than by header values subject to leakage.
• Audit cache behavior with scans that check Authentication, BOLA/IDOR, and Data Exposure findings to detect unsafe caching patterns.