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Shiny, Let's Be Bad Guys: Exploiting and Mitigating the Top 10 Web App Vulnerabilities -- 2015 edition

Shiny, Let's Be Bad Guys: Exploiting and Mitigating the Top 10 Web App Vulnerabilities -- 2015 edition

Slides from the Pycon 2015 presentation of our tutorial that walks through the OWASP Top 10 web application vulnerabilities.


Mike Pirnat

April 08, 2015


  1. Shiny Let’s Be Bad Guys! Exploiting and Mitigating the Top

    1 0 Web App Vulnerabilities Mike Pirnat David Stanek - @mpirnat - @dstanek PyCon 2015
  2. Announcements

  3. Schedule • This session will run 9:00 AM - 12:20

    PM • 20-minute break at ~10:15 AM • Refreshments right outside • Lunch in room 710
  4. Tutorial Feedback • Via the Guidebook app • Look for

    the Tutorial Survey link in the talk details • Be honest! :-)
  5. Volunteering Opportunities • Low-commitment! Fun! • Swag bagging: Thursday 3-6

    PM • Registration Desk: any time • https://us.pycon.org/2015/about/ volunteers/
  6. Shiny Text Let’s Be Bad Guys! Exploiting and Mitigating the

    Top 1 0 Web App Vulnerabilities Mike Pirnat David Stanek - @mpirnat - @dstanek
  7. http://i.qkme.me/3r16r5.jpg

  8. Who here makes web apps?

  9. Who here has vulnerable apps?

  10. Why it Matters • Your users • Your data •

    Your business
  11. OWASP • http://www.owasp.org • Open Web Application Security Project •

    Non-profit focused on improving software security • Documentation and tools to help learn about security and protect your apps
  12. OWASP Top Ten • Based on risk data from 8

    firms • Over 500,000 vulnerabilities, hundreds of orgs, thousands of apps • Selected & prioritized by prevalence data combined with estimates of exploitability, detectability, and impact • Updated in 2013
  13. Today • Background on a type of vulnerability • Exploit

    it! • Discuss prevention • Django & Flask specific advice where possible • Light examples where we have time
  14. Disclaimer

  15. About Django

  16. Setup: 1 Make & activate a virtualenv: # Python 3...

    $ pyvenv badguys # Python 2... $ virtualenv badguys $ cd badguys $ source bin/activate
  17. Setup: 2 Clone our repository: $ git clone https://github.com/ mpirnat/lets-be-bad-guys

    src Or pull the latest changes: $ cd src $ git pull
  18. Setup: 3 Install dependencies: $ cd src $ pip install

    -r requirements.txt
  19. Setup: 4 Start up the app: $ python manage.py runserver

  20. Find a Partner

  21. Injection

  22. Injection Attacks • When an application sends untrusted data to

    an interpreter • Can result in data loss/corruption, lack of accountability, denial of access • Can lead to complete host takeover
  23. Trust No One • External users • Internal users •

  24. Attack Vectors • GET parameters • POST parameters • PATH_INFO

    • Some HTTP headers: Cookie, Host • Uploaded Files
  25. Possible Consequences • Creation of malicious SQL (or other queries)

    • Accessing private files on disk • Arbitrary code execution
  26. Real-World Examples • Sony Playstation Network • Ruby on Rails

    • http://es.pn/Z0jnoi
  27. SQL Injection • Unescaped user input causes the premature end

    of a SQL query and allows a malicious query to be executed... """ select * from users where username='%s'; """ • http://localhost:8000/injection/sql
  28. Accessing Private Files • File system access + unvalidated user

    input allows attackers to navigate the file system • http://localhost:8000/injection/file- access
  29. Arbitrary Code Execution • Unsafe input is dynamically evaluated or

    executed • http://localhost:8000/injection/code- execution
  30. Prevention • Validate ALL user input • Sign cookies, don’t

    accept if signature is bogus/missing • Use ORMs or bind variables when talking to the database • Don’t use eval or exec, beware of pickle, user-supplied YAML, etc.
  31. Django Advice • Make sure data types for your model

    are tight • Use Forms instead of ModelForms for stronger validation • Make new validators as needed for your application • Make sure your URL regexes for dynamic URLs are tight
  32. Django Advice • Use the ORM when you can •

    When you can’t, use extreme caution! • Bind variables • No string concatenation/formatting of anything that came from the client
  33. Without the ORM # If it's a basic select: MyModel.objects.raw("SELECT

    ... WHERE foo = %s", params={'foo': ...}) # If it's more complicated: from django.db import connection cursor = connection.cursor() cursor.execute("UPDATE bar set bar = 1 WHERE foo < %s", [foo]) row = cursor.fetchall()
  34. Flask Advice • Use Flask-WTF to validate form input •

    Use SQLAlchemy • Bind variables if you don’t
  35. Broken Authentication & Session Management

  36. Broken Auth & Session Management • Attacker uses leaks or

    flaws in authentication or session management to impersonate users • Roll-your-own solutions contribute to the difficulty of finding these flaws
  37. Possible Consequences • Compromised user accounts • Compromised administrative accounts

    • Unauthorized use of privileged functionality
  38. Prevention • Hash or encrypt passwords • Don’t let credentials

    be easily overwritten • Don’t put session IDs in URLs • Allow session IDs to timeout/log out • Rotate session IDs after successful login • TLS connections for passwords, session IDs
  39. Django Advice • Use django.contrib.auth • Consider https://github.com/yourlabs/ django-session-security middleware

    for timing out sessions • We’ll talk about transport layer security later on...
  40. Flask Advice • Use flask-security • https://pythonhosted.org/Flask-Security/ • Avoid overuse

    of cookies for storing session state
  41. Cross-Site Scripting (XSS)

  42. XSS Attacks • Cross-Site Scripting (XSS) • The most prevalent

    web app security flaw • App includes user-supplied data in content sent to the browser without properly validating or sanitizing it
  43. XSS Attacks • Stored: injected code permanently stored in database,

    message forum, comment, etc. • Reflected: injected code in live request to server, reflected back in error message or search result • DOM: injected code in browser DOM environment that causes scripts to run in unexpected ways (eg, reading from URL)
  44. Possible Consequences • Execute scripts in a victim’s browser •

    Hijack sessions • Deface sites • Insert hostile content • Redirect users • Hijack browser (install malware)
  45. Most Often Seen... • Places where user-created text is displayed

    to other users (comments, messages) • Form inputs where value is populated with user-supplied data • Script tags where user-supplied data is populated into script variables
  46. XSS in Dynamic URLs • Part of the URL path

    is variable, isn’t validated, and gets included into the page • http://localhost:8000/cross-site- scripting/path-matching/your-path- here
  47. XSS in Query String Parameters • Unvalidated user input from

    a query string parameter is included in the page • http://localhost:8000/cross-site- scripting/query-params?qs=awesome
  48. XSS in Form Fields • The value part of an

    input is prematurely terminated, allowing Javascript to be injected into the element (eg, adding an onclick) • http://localhost:8000/cross-site- scripting/form-field
  49. Can you trust the database?

  50. Prevention • Escape all untrusted data based on the HTML

    context the data will be placed into • Whitelist input validation • Consider auto-sanitization libraries for rich content (eg, OWASP’s AntiSamy) • Update your parents’/in-laws’ browsers!
  51. Django Advice • Be careful with the safe filter, django.utils.safestring,

    etc. • Use form.as_p, form.as_table, form.as_ul when displaying a form in a template • Be careful with your own template tags; django.utils.html.escape is your friend!
  52. django.utils.html cleaned = escape(unsafe_value) cleaned = escapejs(unsafe_value) cleaned = strip_tags(unsafe_value)

    cleaned = remove_tags(unsafe_value, ['script', ...])
  53. Flask Advice • Don’t disable autoescaping • Be very careful

    with anything you bless via Markup objects, the safe filter, or blocks where autoescape is disabled
  54. Insecure Direct Object References

  55. Insecure Direct Object Reference • Expose a reference to an

    internal implementation object without verifying authorization • Attacker changes URL or GET/POST parameters, cookies
  56. Possible Consequences • Compromise of all data that can be

    referenced by the vulnerable parameter • Unless the namespace is sparse, an attacker can easily access all available data of that type
  57. Exercises • Manipulate parameters in the URL to access data

    that doesn’t belong to you • http://localhost:8000/direct-object- references
  58. Prevention • Implement access controls on any direct references to

    restricted resources • Implement per-user or per-session indirect object references • This can be as much about URL design as about access control!
  59. Django + Flask • Lock down views: • Use Django’s

    permissions architecture • Use Flask-Security or Flask-Login • Customize Django queryset for looking up objects that involve user ownership
  60. Custom Queryset # In models.py... class ThingyManager(models.Manager): def for_user(self, user):

    return self.get_query_set().filter(user=user) class Thingy(models.Model): objects = ThingyManager() # In views.py... class ThingyUpdateView(UpdateView): def get_queryset(self): return Thingy.objects.for_user( self.request.user)
  61. Security Misconfiguration

  62. Security Misconfiguration • Insecure application settings • Unpatched flaws •

    Unused pages
  63. Possible Consequences • Unauthorized access to some system data or

    functionality • Potential complete system compromise
  64. Exercises • Demos and discussion • http://localhost:8000/misconfiguration

  65. Prevention • Have a repeatable hardening process • Have a

    process for keeping on top of updates and patches • Architecture that provides secure separation between components • Periodic scans and audits
  66. Django Advice • Don’t run in debug mode in production

    • Keep your SECRET_KEY secret! • Keep Python code out of webserver’s root • Don’t run admin publicly (if you can help it) • Don’t use the built-in admin for normal user admin tasks
  67. Flask Advice • Read http://flask.pocoo.org/docs/ security • Set app.debug =

    False to turn off debugging
  68. Gateway to Social Engineering?

  69. Sensitive Data Exposure

  70. Sensitive Data Exposure • Failure to properly protect credit cards,

    tax ids, authentication credentials, etc. • Sensitive data deserves extra protection such as encryption at rest or in transit, special precautions when exchanged with the browser
  71. Insecure Cryptographic Storage • Not encrypting worthy data • Unsafe

    key generation & storage, failure to rotate keys • Weak algorithms • Weak or unsalted hashes
  72. Insufficient Transport Layer Protection • May not authenticate, encrypt, and

    protect the confidentiality and integrity of sensitive network traffic • May use weak algorithms • May use expired or invalid certificates • May use certificates incorrectly
  73. Possible Consequences • Compromise of all data that should have

    been encrypted • This can be highly sensitive information: credentials, credit cards, personal data, health records, etc.
  74. Possible Consequences • Expose individual users’ data • Account theft

    • Compromise an admin account?! • Poor SSL setup can facilitate phishing and man-in-the-middle attacks
  75. Attack Vectors • Attacker monitors network traffic of your users

    • Maybe in public places (Starbucks, conference wi-fi, etc.) • Maybe back end connections • Maybe inside your network (!!!)
  76. Prevention • Encrypt sensitive data at rest • Encrypt offsite

    backups; manage keys separately • Use strong standard algorithms, strong keys • Hash passwords with strong standard algorithm & use appropriate salt • Protect passwords & keys from unauthorized access
  77. Prevention • Require SSL for all sensitive pages; redirect non-SSL

    requests to SSL • Set the “secure” flag on sensitive cookies • Use only strong SSL algorithms • Ensure your cert is valid, not expired, not revoked, and matches your domain • SSL/encryption on the back end too
  78. Django Advice • Use django.contrib.auth for proper password salting and

    hashing • Use bcrypt; see https://docs.djangoproject.com/en/ 1.8/topics/auth/passwords/ • Require SSL in Apache or Nginx • Require SSL using middleware: • Configure Django SecurityMiddleware–new in Django 1.8! • http://django-secure.readthedocs.org/en/v0.1.2/ • https://github.com/rdegges/django-sslify
  79. Secure Cookies # In your settings.py... SESSION_COOKIE_SECURE = True CSRF_COOKIE_SECURE

    = True
  80. Flask Advice • Salt passwords using werkzeug.security: • http://flask.pocoo.org/snippets/54/ •

    Require SSL: • https://github.com/kennethreitz/flask-sslify • https://github.com/jacobian/wsgi-sslify • Use bcrypt; see https://pythonhosted.org/ passlib/
  81. Missing Function Level Access Control

  82. Missing Function Level Access Control • Application doesn’t protect its

    functions properly • Misconfiguration • Forgot proper code checks
  83. Attack Vectors • Authorized user changes a URL or parameter

    to a privileged function • Anonymous users could access private functions that aren’t protected
  84. Possible Consequences • Compromised user accounts • Compromised administrative accounts

    • Unauthorized use of privileged functionality
  85. Exercises • Manipulate the URL to access privileged functionality •

    http://localhost:8000/missing-access- control
  86. Prevention • Consider every page; public or private? • If

    authentication is required, make sure that checks are in place • If additional authorization is required, make sure that checks are in place • Deny all by default; explicitly grant access to users or roles
  87. Django + Flask • Lock down views: • Use Django’s

    permissions architecture • Use Flask-Security or Flask-Login • Don’t use Django’s built-in admin for normal user admin tasks
  88. Cross-Site Request Forgery

  89. CSRF Attacks • Cross-Site Request Forgery (CSRF) • Attacker tricks

    victim into submitting forged HTTP requests • Attack succeeds if user is authorized/ authenticated
  90. Attack Vectors • Image tags • Cross-Site Scripting (XSS) •

    Fake buttons • Phishing forms • Other techniques
  91. Possible Consequences • Cause victim to change any data the

    victim is allowed to change • Cause victim to perform any function the victim is authorized to use • Impact varies based on victim’s role • Think of some possibilities...
  92. Real-World Examples • Facebook: http://amolnaik4.blogspot.com/ 2012/08/facebook-csrf-worth- usd-5000.html • Google/Gmail: http://cryptogasm.com/2012/02/does-

  93. CSRF via Image • Craft an “image” link that triggers

    some site functionality • http://localhost:8000/csrf/image
  94. What if... <img src="http://example.com/transferFunds?amount=1500& destinationAccount=attackersAcct#" width="0" height="0" />

  95. CSRF via Form Post • Create an innocuous-looking form that

    POSTs to a vulnerable location • http://localhost:8000/csrf/third-party- site
  96. Prevention • Don’t “do” things on a GET • Include

    a unique token in a hidden field (often used in concert with a cookie) • Validate token to make sure the request is from on-site • Avoid putting the token into a query string
  97. Django Advice • Don’t change the built-in settings! • Do

    use the CSRF middleware and template tag in forms • Be VERY CAREFUL about deactivating it (csrf_exempt decorator) • Be careful about APIs (Tastypie, oauth); http://codrspace.com/vote539/csrf- protection-in-django-tastypie/
  98. Flask Advice Various CSRF solutions... • DIY/naïve: http://flask.pocoo.org/snippets/3/ • Flask-WTF:

    http://flask-wtf.readthedocs.org/ en/latest/csrf.html • Flask-SeaSurf: https://flask- seasurf.readthedocs.org/en/latest/ • Flask-csrf: http://sjl.bitbucket.org/flask-csrf/
  99. Using Known Vulnerable Components

  100. Components with Known Vulnerabilities • Libraries, frameworks, and other modules

    almost always run with full privilege • Hard to stay up to date on everything • Do you even know all the components in use, let alone their versions? • Components with known problems can be identified & exploited with automated tools
  101. Attack Vectors • Attacker identifies a weak component through scanning

    or manual analysis • Customize exploit as needed • More difficult the deeper the component is in the application
  102. Possible Consequences • Full range of weaknesses are possible •

    Impact could be minimal, or... • Complete host takeover! • Data compromise!
  103. None
  104. None
  105. None
  106. None
  107. None
  108. Prevention • Don’t use components you don’t write (unrealistic) •

    Keep components up to date • Identify all components and versions • Monitor security of these components
  109. Python Advice • Use pip to find old packages: pip

    list --outdated • Use requires.io to monitor dependencies
  110. Django + Flask • Keep an eye on the mailing

    lists: • https://groups.google.com/group/django- announce • http://flask.pocoo.org/mailinglist • Follow @djangoproject on Twitter
  111. Unvalidated Redirects & Forwards

  112. Redirection Abuse • Attacker tricks user into visiting a URL

    that redirects or forwards the request without validating the redirect location • Users prone to click because the link is to a legitimate site
  113. Possible Consequences • Install malware • Phishing/information disclosure • Bypass

    access controls
  114. External Redirection • Use a redirection URL to redirect to

    an external location • http://localhost:8000/redirects-and- forwards/redirects
  115. Forwards • Manipulate a forward parameter to gain access to

    privileged functionality • http://localhost:8000/redirects-and- forwards/forwards
  116. Prevention • Don’t use redirects or forwards • Don’t involve

    user-supplied data to build the redirect location • Ensure the supplied value is valid and authorized for the user
  117. Django Advice • Use django.utils.http.is_safe_url to check redirect URLs •

    Used by django.contrib.auth internally • Consider wrapping is_safe_url if you have to allow other off-domain URLs
  118. Checking Redirects from django.shortcuts import redirect from django.utils.http import is_safe_url

    def my_view(request): ... url = 'http://www.example.com/foo/bar' if is_safe_url(url, host='www.example.com'): return redirect(url) else: ...
  119. Allowing Multiple Safe Hosts from django.utils.http import is_safe_url def is_whitelisted_url(url,

    hosts): for host in hosts: if is_safe_url(url, host=host): return True return False >>> url = 'http://us.pycon.org' >>> whitelist = ['us.pycon.org', 'pycon.org', ...] >>> is_whitelisted_url(url, whitelist) True
  120. Flask Advice • Redirect back: http://flask.pocoo.org/ snippets/62/ • Redirect back,

    more selectively with whitelist, using cookies for previous URL: http://flask.pocoo.org/snippets/120/ • Can modify these approaches to suit, as with the Django example
  121. Who here has vulnerable apps?

  122. Parting Thoughts

  123. Think Like a Bad Guy

  124. Don’t Stop at Ten

  125. Constant Change

  126. Think Positive

  127. Announcements • Feedback! Via Guidebook • Volunteer! https://us.pycon.org/2015/ about/volunteers/ •

    Lunch! Room 710
  128. Links • http://www.owasp.org • https://www.owasp.org/index.php/ Category:OWASP_Top_Ten_Project • https://docs.djangoproject.com/en/dev/ topics/security/ •

  129. Contact Us Mike Pirnat http://mike.pirnat.com @mpirnat David Stanek http://traceback.org @dstanek