Cache Poisoning in Gorilla Mux with Cockroachdb

Cache poisoning occurs when an attacker manipulates cached responses so that subsequent users receive malicious or incorrect data. When using Gorilla Mux as a router in front of services that rely on CockroachDB, the risk arises from a mismatch between route-driven caching logic and the database identity provided in requests. Gorilla Mux allows you to define variables in routes, such as /{tenant_id}/data, and these variables are often used to construct cache keys. If the caching layer uses only parts of the request—such as the path prefix—and does not properly validate or scope by authenticated tenant or user identifiers stored in CockroachDB rows, an attacker can request /1001/data while the cache key for tenant 1002 is reused, effectively reading another tenant’s data.

In a typical setup, a handler might query CockroachDB with a SQL condition like WHERE tenant_id = $1, using the Gorilla Mux variable mux.Vars(request)["tenant_id"]. If the application caches the database rows keyed only by the URL path, a request for /1001/data might return cached rows belonging to tenant 1001, while the SQL query for tenant 1002 is never executed but the cache is still considered valid. This is a BOLA/IDOR pattern enabled by the interaction between route parameters and CockroachDB row-level permissions. CockroachDB itself enforces SQL-level consistency and isolation, but it does not prevent an application from constructing incorrect cache keys that ignore tenant boundaries defined in the database schema. Without explicit tenant scoping in cache logic, the database’s correctness does not translate to application-level confidentiality or integrity.

Additionally, if the application caches error responses or metadata (such as schema or table listings) that include tenant-specific identifiers, an attacker can probe routes to infer valid tenant IDs via timing or cache hit ratios. Because Gorilla Mux routes are static patterns and Cockroachdb stores rows with explicit tenant identifiers, any caching layer must include both the route parameters and the authenticated principal (often derived from a row in CockroachDB) when forming cache keys. Failure to do so exposes a discrepancy where the route appears correct but the underlying data context is polluted across users.

To remediate cache poisoning, enforce tenant scoping at both the database query and the caching layer. In Gorilla Mux, extract the route variable and ensure every CockroachDB query includes it as a parameter, while also incorporating the authenticated user or tenant identifier into the cache key. Below is a concrete example using the pgx driver with CockroachDB and a simple in-memory cache that respects tenant boundaries.

// main.go
package main

import (
    "context"
    "fmt"
    "net/http"
    "github.com/gorilla/mux"
    "github.com/jackc/pgx/v5/pgxpool"
)

type App struct {
    db    *pgxpool.Pool
    cache map[string][]byte // simplistic cache keyed by string
}

func (a *App) getData(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    tenantID := vars["tenant_id"]
    userID := r.Header.Get("X-User-ID") // or extract from JWT
    cacheKey := fmt.Sprintf("tenant:%s:user:%s:data", tenantID, userID)

    if val, ok := a.cache[cacheKey]; ok {
        w.Write(val)
        return
    }

    ctx := context.Background()
    rows, err := a.db.Query(ctx, `SELECT id, payload FROM tenant_data WHERE tenant_id = $1`, tenantID)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    defer rows.Close()

    var results []byte // serialized rows; in practice, use JSON or protobuf
    // iterate and serialize ...
    a.cache[cacheKey] = results
    w.Write(results)
}

func main() {
    connPool, err := pgxpool.New(context.Background(), <your-cockroachdb-connection-string>)
    if err != nil {
        panic(err)
    }
    app := &App{db: connPool, cache: make(map[string][]byte)}
    r := mux.NewRouter()
    r.HandleFunc("/{tenant_id}/data", app.getData).Methods("GET")
    http.ListenAndServe(":8080", r)
}

The key remediation points are:

• Include both the Gorilla Mux route variable (tenant_id) and a user or session identifier (e.g., X-User-ID or a claim from authentication) in the cache key. This ensures that tenant 1001’s cached data cannot be served to tenant 1002 even if their URL paths are structurally similar.
• Always parameterize CockroachDB queries with the route variable as a bound argument ($1), preventing accidental string concatenation that could lead to SQL injection or tenant leakage.
• Validate that the authenticated principal has access to the requested tenant by checking a row in CockroachDB (e.g., a membership table) before returning cached or fresh data. This enforces tenant-level permissions at runtime, complementing the database’s row-level isolation.

For production, replace the in-memory map with a distributed cache that supports namespacing (e.g., Redis keys prefixed by tenant ID). Continue to pass the tenant ID as a CockroachDB parameter in every query, and ensure that cache invalidation respects tenant boundaries to avoid cross-tenant data exposure.