Pii Leakage in Buffalo with Basic Auth

Buffalo is a popular Go web framework that simplifies routing, parameter parsing, and response rendering. When Basic Auth is used in Buffalo without additional protections, PII leakage can occur because credentials are transmitted in an easily decoded format and may be inadvertently exposed in logs, error messages, or downstream outputs.

Basic Auth encodes credentials using Base64, which is reversible and provides no encryption. If a Buffalo application sends credentials only via Basic Auth over non-TLS transport, an on-path attacker can decode the header and obtain usernames and passwords. Even over TLS, improper handling of credentials in Buffalo handlers or middleware can lead to PII leakage through server logs, panic traces, or debug output.

Consider a Buffalo action that retrieves a user profile and includes the authenticated username in a JSON response without careful filtering:

app.Get("/profile", func(c buffalo.Context) error {
    user, _ := c.Value(&models.User{}).(*models.User)
    // Risk: including raw user fields that may contain PII
    return c.Render(200, r.JSON(user))
})

If the User model contains fields such as Email, PhoneNumber, or NationalID, and no explicit field filtering is applied, the response can leak PII. MiddleBrick’s LLM/AI Security checks include Output scanning for PII and would flag exposed email or phone values in API responses, which is relevant when Buffalo APIs are consumed by AI-enabled clients.

Another scenario involves error handling. Buffalo’s default HTML or JSON error rendering might include request parameters that contain PII. For example:

app.Params.Add("email", "user@example.com")
app.Params.Add("ssn", "123-45-6789")
// Risk: parameters may appear in logs or error pages
app.Render(500, r.HTML("errors/internal", buffalo.X{"params": c.Params()}))

Here, sensitive parameters could be logged in plaintext by application or server logging middleware, leading to PII leakage. middleBrick’s Data Exposure checks are designed to detect such risky outputs and to map findings to frameworks like OWASP API Top 10 and GDPR.

When combined with unauthenticated scanning, which is a default mode in middleBrick, these exposures can be identified without credentials. middleBrick’s cross-referencing of OpenAPI specs with runtime findings helps highlight endpoints where PII-bearing parameters are returned without proper authorization controls.

To reduce PII leakage risk in Buffalo applications using Basic Auth, enforce transport security, avoid logging credentials, and apply strict output filtering.

1. Enforce TLS and avoid sending credentials in plaintext

Always serve Buffalo applications over HTTPS. Use middleware to redirect HTTP to HTTPS and ensure the Authorization header is never logged.

// main.go
package app

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

func App() *buffalo.App {
    if Env() == buffalo.EnvProd {
        app := buffalo.New(buffalo.Options{
            PreWares: []buffalo.PreWare{
                middleware.ForceSSL,
            },
        })
        return app
    }
    // local development without forced SSL
    app := buffalo.New(buffalo.Options{})
    return app
}

2. Securely handle Basic Auth credentials

Use middleware to validate credentials without exposing them in logs. Avoid passing raw credentials into Buffalo context values that might be serialized.

// auth_middleware.go
package middleware

import (
    "net/http"
    "encoding/base64"
    "strings"
)

func BasicAuth(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        auth := r.Header.Get("Authorization")
        if auth == "" {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        const prefix = "Basic "
        if !strings.HasPrefix(auth, prefix) {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        payload, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
        if err != nil {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        parts := strings.SplitN(string(payload), ":", 2)
        if len(parts) != 2 || !valid(parts[0], parts[1]) {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        // Safe: store only a user identifier, not the password
        ctx := context.WithValue(r.Context(), "userID", parts[0])
        next.ServeHTTP(w, r.WithContext(ctx))
    }
}

func valid(user, pass string) bool {
    // validate against a secure store
    return user == "alice" && pass == "correct-hashed-password"
}

3. Filter PII in responses

Use explicit serialization to exclude sensitive fields. Do not rely on automatic struct serialization when returning user data.

// user_profiles.go
package actions

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/validate/v3"
)

type SafeUser struct {
    ID    string `json:"id"`
    Name  string `json:"name"`
    Role  string `json:"role"`
    // Email intentionally omitted to prevent PII leakage
}

app.Get("/profile", func(c buffalo.Context) error {
    user := &models.User{}
    if err := c.Value(user); err != nil {
        return c.Render(400, r.JSON(buffalo.Error{Message: err.Error()}))
    }
    safe := SafeUser{
        ID:   user.ID,
        Name: user.Name,
        Role: user.Role,
    }
    return c.Render(200, r.JSON(safe))
})

4. Avoid leaking parameters in error pages and logs

Configure Buffalo to exclude sensitive parameters from logs and error payloads. Use custom error handlers that strip PII before rendering.

// error_handler.go
package actions

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

func ErrorHandler(c buffalo.Context, err error) error {
    // Log only non-sensitive metadata
    c.Response().Header().Set("X-Error-Handled", "true")
    // Render a generic error without parameters
    return c.Render(500, r.JSON(map[string]string{"error": "internal server error"}))
}

5. Combine with middleBrick scans

Use the middleBrick CLI to validate that PII leakage is not present after remediation:

$ middlebrick scan https://api.example.com

The scan will report findings across 12 checks, including Data Exposure and LLM/AI Security, helping you confirm that PII is not exposed in API responses.