Dns Rebinding in Buffalo with Cockroachdb

Dns rebinding is a client-side attack where a malicious webpage causes a victim’s browser to bypass same-origin policy by changing the DNS resolution of a hostname from a public address to a private IP address. In a Buffalo application that serves an API or admin interface and connects to a Cockroachdb cluster, this can expose internal database endpoints or administrative handlers to an attacker-controlled page.

When Buffalo is used with Cockroachdb, the typical risk pattern is a server-side or client-side route that accepts a hostname or connection string from user input or environment configuration without adequate origin validation. If an attacker can trick a logged-in operator or an embedded admin UI into making a request to a rebinded hostname (e.g., via a crafted link or iframe), the request may reach a Cockroachdb HTTP/status endpoint, an internal admin RPC, or a database proxy that would otherwise be unreachable from the public internet. Because Buffalo does not inherently restrict outbound connections to private IP ranges, a compromised route or misconfigured CORS policy can allow a browser-embedded script to reach internal Cockroachdb HTTP endpoints or backend handlers, leading to unauthorized introspection or, in misconfigured deployments, data exposure.

The exposure is compounded when Cockroachdb’s Admin UI or HTTP endpoints (such as /_status/vars or /debug/vars) are accidentally exposed behind the same host as the Buffalo app, or when reverse proxy rules do not block private IPs. A Buffalo app that dynamically builds database connection strings based on request headers or subdomains can be tricked into connecting to a rebinded IP if input validation is weak. For example, an endpoint that accepts a tenant identifier and constructs a Cockroachdb connection string without restricting private addresses may inadvertently route queries to an internal address after a dns-rebind redirect.

To illustrate, consider a route that forms a Cockroachdb SQL connection using a host provided by the caller:

// WARNING: Unsafe — host controlled by caller
connStr := fmt.Sprintf("postgresql://root@%s:26257/defaultdb?sslmode=disable", r.Host)
db, err := gorm.Open(postgres.Open(connStr), &gorm.Config{})
if err != nil {
    app.Logger.Error("failed to connect", "error", err)
    return errors.New("invalid connection")
}

If this route is reachable from a browser context that an attacker can influence, a rebinding attack can redirect the request to an internal IP such as 127.0.0.1 or a Cockroachdb node, bypassing firewall rules. Even if the app uses environment-based configuration, a compromised subdomain or header can still lead to unintended connections when combined with poor input validation.

Buffalo does not perform network-level filtering, so developers must ensure that any user-influenced host or port used to form Cockroachdb connections is normalized against a strict allowlist of expected endpoints and that private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are rejected. CORS policies should restrict origins strictly, and reverse proxy configurations should block requests targeting internal addresses.

Remediation centers on strict validation of any host or connection parameters and ensuring that Cockroachdb endpoints are never directly controllable by the client. Use a fixed configuration for database connections and avoid dynamic host assembly based on request data. If multiple clusters are required, use server-side mapping with an allowlist.

First, define allowed database endpoints in configuration and resolve them at startup. Do not accept host overrides from requests.

// config/database.go
package config

import (
    "os"
)

var AllowedDBHosts = map[string]bool{
    "prod.cockroach.example.com": true,
    "staging.cockroach.example.com": true,
}

func DatabaseURL() (string, error) {
    url := os.Getenv("COCKROACH_URL")
    if url == "" {
        return "", errors.New("missing COCKROACH_URL")
    }
    // Ensure the URL resolves to an allowed host (simplified check)
    // In production, use net.Resolver and validate against AllowedDBHosts
    return url, nil
}

In your Buffalo app, use this fixed URL to open the connection once, typically in actions/app.go:

// actions/app.go
package actions

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo-pop/pop"
    "yourproject/config"
    "github.com/jackc/pgx/v5/stdlib"
    "database/sql"
    _ "github.com/lib/pq"
)

var DB *pop.Connection

func App() *buffalo.App {
    if DB == nil {
        url, err := config.DatabaseURL()
        if err != nil {
            panic(err)
        }
        db, err := pop.Connect("postgres", url)
        if err != nil {
            panic(err)
        }
        DB = db
    }
    // App initialization...
    return app
}

For multi-tenant routing where a logical mapping is required (e.g., tenant subdomain to Cockroachdb database name), map subdomains to predefined database names server-side, and do not inject them into connection strings derived from the request. Use a switch or map lookup:

// actions/tenant.go
package actions

import (
    "net/http"
    "strings"
)

func TenantDBConnection(r *http.Request) (*pop.Connection, error) {
    host := r.Host // e.g., tenant1.example.com
    tenant := strings.Split(host, ".")[0]
    allowed := map[string]string{
        "tenant1": "tenant1_db",
        "tenant2": "tenant2_db",
    }
    dbName, ok := allowed[tenant]
    if !ok {
        return nil, errors.New("unknown tenant")
    }
    connStr := fmt.Sprintf("postgresql://root@%s:26257/%s?sslmode=disable", "prod.cockroach.example.com", dbName)
    return pop.Connect("postgres", connStr)
}

Additionally, enforce network-level protections in your deployment: ensure Cockroachdb HTTP endpoints are not exposed publicly and that firewall rules block inbound access to internal IPs from web-facing hosts. In Buffalo templates or API handlers, avoid echoing hostnames or origins without strict validation, and set restrictive CORS headers.

Finally, test your configuration with tools that simulate rebinding (e.g., local DNS rebinding proxies) against your Buffalo routes to confirm that internal endpoints remain unreachable. Combine these practices to eliminate the window for dns rebinding against Cockroachdb in Buffalo applications.