Ruby Rails Open Redirect Vulnerability (Brakeman Check)

Medium Risk Open Redirect

RubyRailsOpen RedirectBrakemanURL ValidationPhishing

What it is

Application uses redirect_to with user-controlled URLs in Rails, enabling open redirect attacks that can be exploited for phishing and malicious redirections.

Language:

class SessionsController < ApplicationController
  def create
    user = User.authenticate(params[:email], params[:password])
    
    if user
      session[:user_id] = user.id
      
      # Vulnerable: User controls redirect destination
      redirect_url = params[:redirect_url] || root_path
      redirect_to redirect_url  # Open redirect vulnerability
    else
      flash[:error] = 'Invalid credentials'
      render :new
    end
  end
  
  def logout
    session.clear
    
    # Vulnerable: External redirect after logout
    return_url = params[:return_url]
    redirect_to return_url || login_path
  end
end

class ApplicationController < ActionController::Base
  def redirect_after_action
    # Vulnerable: Dynamic redirect without validation
    next_page = request.referer || params[:next]
    redirect_to next_page
  end
end

class SessionsController < ApplicationController
  ALLOWED_REDIRECT_HOSTS = [
    'app.example.com',
    'secure.example.com',
    'api.example.com'
  ].freeze
  
  def validate_redirect_url(url)
    return root_path if url.blank?
    
    begin
      uri = URI.parse(url)
      
      # Allow relative URLs
      if uri.relative?
        # Ensure it's a path, not a protocol-relative URL
        return url if url.start_with?('/')
        return "/#{url}" unless url.start_with?('//')
        raise ArgumentError, 'Protocol-relative URLs not allowed'
      end
      
      # For absolute URLs, check host allowlist
      if uri.absolute?
        unless uri.scheme.in?(%w[http https])
          raise ArgumentError, 'Invalid URL scheme'
        end
        
        unless ALLOWED_REDIRECT_HOSTS.include?(uri.host)
          raise ArgumentError, 'Host not in allowlist'
        end
        
        return url
      end
      
      raise ArgumentError, 'Invalid URL format'
      
    rescue URI::InvalidURIError
      raise ArgumentError, 'Malformed URL'
    end
  end
  
  def safe_redirect_to(url, fallback = root_path)
    begin
      safe_url = validate_redirect_url(url)
      redirect_to safe_url
    rescue ArgumentError => e
      Rails.logger.warn "Redirect validation failed: #{e.message} for URL: #{url}"
      redirect_to fallback
    end
  end
  
  def create
    user = User.authenticate(params[:email], params[:password])
    
    if user
      session[:user_id] = user.id
      
      # Secure: Validate redirect URL
      redirect_url = params[:redirect_url]
      safe_redirect_to(redirect_url, dashboard_path)
    else
      flash[:error] = 'Invalid credentials'
      render :new
    end
  end
  
  def logout
    session.clear
    
    # Secure: Validate return URL
    return_url = params[:return_url]
    safe_redirect_to(return_url, login_path)
  end
end

class ApplicationController < ActionController::Base
  def redirect_after_action
    # Secure: Use internal routes only
    begin
      # Check if next parameter is a valid internal route
      next_page = params[:next]
      
      if next_page.present?
        # Try to recognize as internal route
        Rails.application.routes.recognize_path(next_page)
        redirect_to next_page
      else
        redirect_to root_path
      end
      
    rescue ActionController::RoutingError
      # Invalid route, redirect to safe default
      redirect_to root_path
    rescue => e
      Rails.logger.error "Redirect error: #{e.message}"
      redirect_to root_path
    end
  end
  
  # Alternative: Use permitted redirect paths
  SAFE_REDIRECT_PATHS = [
    '/dashboard',
    '/profile',
    '/settings',
    '/help'
  ].freeze
  
  def safe_internal_redirect
    requested_path = params[:path]
    
    if SAFE_REDIRECT_PATHS.include?(requested_path)
      redirect_to requested_path
    else
      redirect_to root_path
    end
  end
end

💡 Why This Fix Works

See fix suggestions for detailed explanation.

Why it happens

Rails controller redirects with user input: redirect_to params[:url]. params[:url] user-controlled. Open redirect vulnerability. Attackers craft phishing URLs. redirect_to trusts input without validation. Users redirected to malicious sites appearing legitimate through trusted domain.

Root causes

Using redirect_to with Unvalidated params

Using redirect_to with URL from Request

Redirect based on request data: redirect_to request.referrer or redirect_to params[:return_to]. Referrer and params untrusted. Attackers control redirect destination. OAuth flows vulnerable to redirect manipulation. Post-login redirect exploitation common attack vector.

Not Validating Redirect URLs Against Allowlist

Missing URL validation: url = params[:destination]; redirect_to url. No check if URL within application or trusted domains. External redirects without validation. Allowlist approach not implemented. Any URL accepted for redirection.

Using only_path Without Additional Validation

Partial validation with only_path: redirect_to params[:path], only_path: true. only_path: true prevents full URLs but still allows manipulation. Path can be any route. External redirect still possible with //evil.com syntax. only_path insufficient protection alone.

Building Redirect URLs with String Interpolation

Constructing URLs: redirect_to "/dashboard?next=#{params[:page]}". String interpolation with params. Crafted values like /dashboard?next=//evil.com. URL parsing ambiguities. String building creates injection points for open redirects.

Fixes

Validate Redirect URLs Against Allowlist of Paths

Allowlist validation: ALLOWED_PATHS = ['/dashboard', '/profile', '/settings']; redirect_path = params[:path]; raise unless ALLOWED_PATHS.include?(redirect_path); redirect_to redirect_path. Explicit allowed paths. No arbitrary redirects. Users choose from predetermined safe destinations.

Use Named Routes Instead of Dynamic URLs

Use route helpers: redirect_to dashboard_path or redirect_to user_profile_path(current_user). Named routes guaranteed internal. No external redirect risk. Controller and route names instead of URLs. Rails routing ensures validity.

Validate URL Scheme and Host

Check URL components: uri = URI.parse(params[:url]); raise unless uri.scheme == 'https' && uri.host == request.host; redirect_to uri.to_s. Parse URL. Validate scheme and host. Ensure same origin. Prevent redirects to external sites.

Use only_path: true with Path Validation

Combine only_path with validation: path = params[:path]; raise unless path.starts_with?('/') && !path.include?('//'); redirect_to path, only_path: true. only_path prevents full URLs. Additional checks for // preventing protocol-relative URLs. Layered approach.

Implement Signed Redirect Tokens

Sign return URLs: redirect_url = verifier.generate(params[:return_to]); later: safe_url = verifier.verify(params[:token]); redirect_to safe_url. Rails message verifier. Cryptographically signed tokens. Tampering detected. Only application-generated URLs accepted.

Run Brakeman to Detect Unsafe Redirects

Use Brakeman scanner: brakeman -A detects redirect vulnerabilities. Review Redirect warnings. Fix flagged redirect_to calls. Automated detection in CI/CD. Regular scans prevent unsafe redirects. Brakeman specifically checks redirect_to with user input.

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Ruby Rails Open Redirect Vulnerability (Brakeman Check)

What it is

💡 Why This Fix Works

Why it happens

Root causes

Using redirect_to with Unvalidated params

Using redirect_to with URL from Request

Not Validating Redirect URLs Against Allowlist

Using only_path Without Additional Validation

Building Redirect URLs with String Interpolation

Fixes

Validate Redirect URLs Against Allowlist of Paths

Use Named Routes Instead of Dynamic URLs

Validate URL Scheme and Host

Use only_path: true with Path Validation

Implement Signed Redirect Tokens

Run Brakeman to Detect Unsafe Redirects

C# ASP.NET Open Redirect from Query Parameter

Information Disclosure via Permissive CORS Configuration

Open Redirect Vulnerability in Express Applications

Authorization bypass from user-controlled URL in redirect_to in Rails

Detect This Vulnerability in Your Code

Ruby Rails Open Redirect Vulnerability (Brakeman Check)

What it is

💡 Why This Fix Works

Why it happens

Root causes

Using redirect_to with Unvalidated params

Using redirect_to with URL from Request

Not Validating Redirect URLs Against Allowlist

Using only_path Without Additional Validation

Building Redirect URLs with String Interpolation

Fixes

Validate Redirect URLs Against Allowlist of Paths

Use Named Routes Instead of Dynamic URLs

Validate URL Scheme and Host

Use only_path: true with Path Validation

Implement Signed Redirect Tokens

Run Brakeman to Detect Unsafe Redirects

Related Vulnerabilities

C# ASP.NET Open Redirect from Query Parameter

Information Disclosure via Permissive CORS Configuration

Open Redirect Vulnerability in Express Applications

Authorization bypass from user-controlled URL in redirect_to in Rails

Detect This Vulnerability in Your Code