Information Disclosure in Buffalo

Information disclosure in Buffalo applications often occurs through error handling, debug information leakage, and improper configuration. When Buffalo panics or encounters errors, the default development stack trace includes sensitive information like database credentials, file paths, and internal structure details that attackers can exploit.

A common vulnerability appears in Buffalo's default error handlers. The development error page shows complete stack traces, database queries, and even environment variables. For example, a simple SQL error might reveal:

// Vulnerable: Default error handler in development mode
func (a *Action) Show(c buffalo.Context) error {
    id := c.Param("id")
    var user User
    err := a.DB.Find(&user, id)
    if err != nil {
        return c.Error(404, err) // Exposes full error details
    }
    return c.Render(200, r.JSON(user))
}

The error handler in development mode returns the raw error, potentially exposing database schema, connection strings, or query structure. This becomes critical when applications are accidentally deployed with GO_ENV=development.

Another Buffalo-specific disclosure vector involves environment variable exposure through improper logging. Buffalo's logger captures request context by default, which can include sensitive headers or authentication tokens:

// Vulnerable: Logging sensitive data
func (a *Action) Create(c buffalo.Context) error {
    var input struct {
        Token string `json:"token"`
    }
    if err := c.Bind(&input); err != nil {
        return err
    }
    log.Debugf("Received token: %s", input.Token) // Logs sensitive data
    return c.Render(200, r.JSON(map[string]string{"status": "ok"}))
}

Buffalo's default logger configuration in development mode logs at debug level, making sensitive data visible in logs that might be accessible to unauthorized users or stored in log aggregation systems.

Detecting information disclosure in Buffalo applications requires both manual code review and automated scanning. middleBrick's black-box scanning approach is particularly effective because it tests the actual running API without requiring source code access.

When scanning a Buffalo API endpoint, middleBrick tests for several information disclosure patterns specific to Go web applications. The scanner sends malformed requests to trigger error responses and analyzes the returned content for sensitive information patterns.

# Scan a Buffalo API endpoint
middlebrick scan https://api.example.com --output json

The scanner specifically looks for:

• Stack traces containing file paths, line numbers, and function names
• Database error messages revealing schema or connection details
• Environment variable exposure in error responses
• Debug information in production responses
• Server version information and framework details
• Internal IP addresses and infrastructure details

For Buffalo applications, middleBrick also analyzes OpenAPI specifications if available. Many Buffalo projects generate Swagger specs that might inadvertently document internal implementation details or expose endpoints that shouldn't be public.

Manual detection in Buffalo involves checking the config/app.go file for error handling configuration and examining middleware chains for logging middleware that might capture sensitive data. The app.Errors() configuration determines how errors are handled across the application.

Remediating information disclosure in Buffalo applications requires proper error handling configuration and careful logging practices. The most critical step is ensuring production environments don't expose debug information.

// config/app.go - Production error handling
func app() *buffalo.App {
    app := buffalo.New(buffalo.Options{
        Env:         ENV,
        SessionName: "_myapp_session",
    })

    if ENV == "production" {
        // Custom error handler for production
        app.Errors.Default = func(status int, err error, c buffalo.Context) error {
            // Log the error internally without exposing details
            log.Errorf("Error %d: %v", status, err)
            
            // Return generic error message
            return c.Render(status, r.JSON(map[string]string{
                "error": "An internal error occurred",
                "status": http.StatusText(status),
            }))
        }
        
        // Disable debug logging in production
        log.SetLevel(log.ERROR)
    }

    return app
}

This configuration ensures that production environments return generic error messages while logging detailed errors internally for debugging purposes.

For logging sensitive data, Buffalo applications should implement request-scoped logging that excludes sensitive headers and parameters:

// Custom middleware to filter sensitive data from logs
func filterSensitiveLogging(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        // Create a copy of the request without sensitive headers
        safeRequest := c.Request().Clone(c.Request().Context())
        safeRequest.Header.Del("Authorization")
        safeRequest.Header.Del("Cookie")
        
        // Store safe request in context for logging
        c.Set("safeRequest", safeRequest)
        
        return next(c)
    }
}

// Use in middleware chain
app.Use(filterSensitiveLogging)

Another Buffalo-specific remediation involves configuring the error middleware stack properly. Buffalo's default error middleware should be customized to prevent information leakage:

// Custom error middleware
func customErrorMiddleware(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        err := next(c)
        if err != nil {
            // Check if error is a typed error we can handle safely
            if typedErr, ok := err.(TypedError); ok {
                return c.Render(typedErr.StatusCode, r.JSON(map[string]string{
                    "error": typedErr.Message,
                }))
            }
            
            // For unknown errors, return generic message in production
            if ENV == "production" {
                log.Errorf("Unhandled error: %v", err)
                return c.Render(500, r.JSON(map[string]string{
                    "error": "Internal server error",
                }))
            }
        }
        return err
    }
}

These remediation strategies ensure that Buffalo applications maintain security while still providing useful debugging information during development.