Security is Broken: Understanding Common Vulnerabilities

Mountain West Ruby Conference

Transcript

1. SECURITY IS BROKEN
   Understanding Common Vulnerabilities
   

   View Slide

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

   View Slide

3. View Slide

4. View Slide

5. OPEN SOURCE
   Rails Committers
   Rails Security
   

   View Slide

6. View Slide

7. View Slide

8. How is security
   broken?
   

   View Slide

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

   View Slide

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

    View Slide

11. • 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?
    

    View Slide

12. How did we get
    here?
    

    View Slide

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

    View Slide

14. vs.
    

    View Slide

15. View Slide

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

    View Slide

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

    View Slide

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

    View Slide

19. View Slide

20. CSRF
    

    View Slide

21. CSRF
    Cross-Site Request Forgery
    

    View Slide

22. EXPLOITING CSRF
    

    View Slide

23. View Slide

24. 
    Name
    
    Email
    
    Website
    
    
    
    

    View Slide

25. View Slide

26. Looks the same, different URL
    

    View Slide

27. 
    
    Name
    
    Email
    
    Website
    
    
    
    
    

    View Slide

28. 
    Name
    
    Email
    
    Website
    
    
    
    Attackers email
    

    View Slide

29. 
    
    Name
    
    Email
    
    Website
    
    
    
    
    Auto-submit form
    

    View Slide

30. 
    
    Name
    
    Email
    
    Website
    
    
    
    
    Auto-submit form
    to victim site
    

    View Slide

31. Attacker’s email
    

    View Slide

32. How dangerous are
    CSRF attacks?
    

    View Slide

33. How to mitigate
    CSRF?
    

    View Slide

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

    View Slide

35. View Slide

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

    View Slide

37. 
    name=authenticity_token" />
    Name
    
    Email
    
    Website
    
    
    
    CSRF protection
    

    View Slide

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

    View Slide

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

    View Slide

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

    View Slide

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

    View Slide

42. View Slide

43. • Use built-in framework CSRF protection
    • Rails 5 supports per-form tokens
    How to mitigate CSRF?
    

    View Slide

44. • Use built-in framework CSRF protection
    • Rails 5 supports per-form tokens
    • Refresh tokens with the session / don’t
    reuse tokens
    How to mitigate CSRF?
    

    View Slide

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

    View Slide

46. • Use built-in framework CSRF protection
    • Rails 5 supports per-form tokens
    • Refresh tokens with the session / don’t
    reuse tokens
    • Mitigate XSS attacks
    How to mitigate CSRF?
    

    View Slide

47. XSS
    

    View Slide

48. XSS
    Cross-Site Scripting
    

    View Slide

49. EXPLOITING STORED
    XSS
    

    View Slide

50. View Slide

51. View Slide

52. Escaped HTML
    

    View Slide

53. Profile
    
    
    Name:
    
    
    
    Email:
    
    
    
    Website:
    
    
    |
    
    

    View Slide

54. Profile
    
    
    Name:
    
    
    
    Email:
    
    
    
    Website:
    
    
    |
    
    

    View Slide

55. Unescaped HTML
    

    View Slide

56. JavaScript Scheme
    

    View Slide

57. View Slide

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

    View Slide

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

    View Slide

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

    View Slide

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

    View Slide

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

    View Slide

63. How dangerous are
    XSS attacks?
    

    View Slide

64. How to mitigate
    XSS?
    

    View Slide

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

    View Slide

66. Profile
    
    
    Name:
    
    
    
    Email:
    
    
    
    Website:
    
    
    |
    
    Don’t do this
    

    View Slide

67. View Slide

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

    View Slide

69. Profile
    
    
    Name:
    
    
    
    Email:
    
    
    
    Website:
    
    
    |
    
    Will strip out unwanted
    tags and attributes
    

    View Slide

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

    View Slide

71. 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
    

    View Slide

72. 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
    

    View Slide

73. 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
    

    View Slide

74. XXE
    

    View Slide

75. XXE
    XML eXternal Entity Attack
    

    View Slide

76. 
    
    
    ]>
    
    Groceries
    Take Arya to the vet
    &ext1;
    Pick up beer
    Get car oil changed
    
    

    View Slide

77. 
    
    
    ]>
    
    Groceries
    Take Arya to the vet
    &ext1;
    Pick up beer
    Get car oil changed
    
    Entity reference
    

    View Slide

78. 
    Book flight to Salt Lake City
    Finish Security is Broken Talk
    

    View Slide

79. 
    
    Groceries
    Take Arya to the vet
    Book flight to Salt Lake City
    Finish Security is Broken Talk
    Pick up beer
    Get car oil changed
    
    

    View Slide

80. EXPLOITING XXE
    with cURL
    

    View Slide

81. 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
    

    View Slide

82. 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
    

    View Slide

83. 
    config/secrets.yml">
    ]>
    
    &name;
    
    

    View Slide

84. 
    config/secrets.yml">
    ]>
    
    &name;
    
    Requested file
    

    View Slide

85. 
    config/secrets.yml">
    ]>
    
    &name;
    
    Entity
    

    View Slide

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

    View Slide

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

    View Slide

88. curl -X 'POST'
    -H 'Content-Type: application/xml'
    -d @xxe.xml
    http://vulnerablesite.com/users.xml
    
    
    ...
    production:
    secret_key_base:
    271a389cf7bf7b4ff18af3e809241603802b5ff1617b5432a41ff0f99d5
    f29c897db7f07a9cebd9e3a3535301720c0b19ac4eb82afa505ed229c40
    00e166a9a5
    ...
    
    
    User’s Name
    

    View Slide

89. View Slide

90. How dangerous are
    XXE attacks?
    

    View Slide

91. View Slide

92. How to mitigate
    XXE?
    

    View Slide

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

    View Slide

94. Don’t parse XML
    

    View Slide

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

    View Slide

96. >> LibXML::XML.default_substitute_entities
    >> true
    

    View Slide

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

    View Slide

98. Investigate vulnerabilities & patches
    SECURITY
    

    View Slide

99. owasp.org
    

    View Slide

100. Resilience & empowerment
     SECURITY
     

     View Slide

101. View Slide

102. GitHub

     eileencodes/security_examples
     

     View Slide

103. Awareness of vulnerabilities
     SECURITY
     

     View Slide

104. View Slide

105. To the future
     

     View Slide

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

     View Slide