Cors Wildcard in Buffalo with Cockroachdb

A CORS wildcard in a Buffalo application that uses CockroachDB can unintentionally expose database-backed endpoints to any origin. When app.ServeMux allows * via middleware.AllowCORS without restricting origins, the browser sends credentials-less requests that may reach handlers constructed over CockroachDB session or transaction logic. Because CockroachDB often stores sensitive relational data, a wildcard that also permits credentials or exposes JSON endpoints can turn a permissive CORS policy into a data exposure vector.

Buffalo routes typically map to handlers that open a CockroachDB connection, perform queries, and render HTML or JSON. If a route like /api/users/:id responds to any origin due to a wildcard, an attacker’s page can issue authenticated-style requests (e.g., via cookies or tokens) and leverage the browser to relay responses. Even though Buffalo does not automatically expose CORS headers, developers sometimes add broad rules during rapid prototyping. Combined with CockroachDB’s role as the authoritative data store, this can inadvertently allow cross-origin reads of user-specific records if authorization checks are missing or inconsistent.

The interaction with CockroachDB becomes risky when preflight responses include Access-Control-Allow-Origin: * alongside credentials-friendly settings. Browsers then permit frontend JavaScript to read responses that may contain database-derived data, such as serialized models or raw JSON from Render calls. If the backend does not validate the Origin header on a per-route basis, the wildcard remains active even for endpoints that execute sensitive CockroachDB queries. This is distinct from authentication flaws; it is a misconfiguration that amplifies impact when the data layer returns personally identifiable information or session-related fields.

In a typical Buffalo + CockroachDB stack, the vulnerability surfaces at the middleware layer before reaching SQL. A developer might enable CORS for local development with a wildcard and forget to tighten it before deploying to production. Because CockroachDB handles distributed SQL with strong consistency, queries executed under a wildcard-origin request can still return rows that should be restricted by tenant or ownership rules. Therefore, the risk is not in CockroachDB itself, but in the absence of origin validation paired with insufficient route-level authorization, turning an otherwise safe database driver into a channel for unintended cross-origin data leakage.

Tools like middleBrick can scan such API configurations and highlight CORS misconfigurations alongside findings from its 12 security checks, including BOLA/IDOR and Data Exposure. By correlating CORS rules with endpoint behavior and database interaction patterns, the scanner provides prioritized findings with remediation guidance. This helps teams ensure that CockroachDB-driven responses are not broadly exposed via permissive CORS policies, and that any use of wildcards is deliberate and limited to non-sensitive routes.

To remediate CORS wildcard issues in a Buffalo app using CockroachDB, start by narrowing CORS configuration to specific origins and applying it selectively. Avoid global wildcards for routes that interact with CockroachDB. Use Buffalo’s middleware registration to scope CORS to trusted origins only, and ensure sensitive routes perform explicit authorization before querying the database.

Example: configure CORS in actions/app.go with a controlled allow-origin list and wrap handlers that execute CockroachDB queries with a custom check:

package actions

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo/middleware"
    "github.com/gobuffalo/packr/v2"
    "net/http"
    "strings"
)

func App() *buffalo.App {
    if app == nil {
        app = buffalo.New(buffalo.Options{
            Env:         ENV,
            SessionStore: &middleware.SessionCookieStore{},
            PreWares: []buffalo.PreWare{
                middleware.ParameterLogger,
                // Configure CORS with specific origins instead of wildcard
                middleware.AllowCORS(&middleware.CORSOptions{
                    AllowedOrigins:   []string{"https://app.example.com", "https://admin.example.com"},
                    AllowedMethods:   []string{"GET", "POST", "OPTIONS"},
                    AllowedHeaders:   []string{"Authorization", "Content-Type"},
                    ExposedHeaders:   []string{"X-Total-Count"},
                    AllowCredentials: true,
                }),
            },
        })

        app.GET("/api/users/:id", withCockroachDBCheck(userShow))
        app.POST("/api/data", withCockroachDBCheck(dataCreate))
    }
    return app
}

// withCockroachDBCheck ensures origin and ownership validation before DB interaction
func withCockroachDBCheck(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        origin := c.Request().Header.Get("Origin")
        allowed := map[string]bool{
            "https://app.example.com": true,
            "https://admin.example.com": true,
        }
        if !allowed[origin] {
            return c.Error(http.StatusForbidden, "invalid origin")
        }
        // Optional: additional tenant or ownership checks using session claims
        return next(c)
    }
}

func userShow(c buffalo.Context) error {
    tx := c.Value("tx").(*pop.PopTransaction)
    var user User
    // CockroachDB query with tenant-aware lookup
    if err := tx.Where("tenant_id = ? AND id = ?", c.CurrentUser().TenantID, c.Param("id")).First(&user); err != nil {
        return c.Error(http.StatusNotFound, err)
    }
    return c.Render(http.StatusOK, r.JSON(user))
}

func dataCreate(c buffalo.Context) error {
    tx := c.Value("tx").(*pop.PopTransaction)
    payload := struct {
        Value string `json:"value"`
    }{}
    if err := c.Bind(&payload); err != nil {
        return err
    }
    // CockroachDB insert with explicit tenant context
    record := Record{
        TenantID: c.CurrentUser().TenantID,
        Value:    payload.Value,
    }
    if err := tx.Create(&record); err != nil {
        return c.Error(http.StatusInternalServerError, err)
    }
    return c.Render(http.StatusCreated, r.JSON(record))
}

In this example, withCockroachDBCheck acts as a guard that validates the Origin header before any CockroachDB interaction occurs. The allowed origins are explicitly listed, preventing wildcard leakage. Within handlers like userShow and dataCreate, queries include a tenant filter derived from the authenticated context, ensuring that even if CORS were misconfigured later, row-level security on the CockroachDB side (via tenant_id) limits exposure.
For broader safety, avoid placing the wildcard globally in actions/app.go. Instead, apply CORS selectively to routes that do not handle sensitive CockroachDB operations. Combine this with runtime scanning using tools like middleBrick to detect any accidental wildcard usage in production configurations and to verify that CORS rules align with your authorization model.