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.

Transcript

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 • Administrators
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- google-understand-csrf/
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!
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/ • https://github.com/mpirnat/lets-be-bad-guys
129. Contact Us Mike Pirnat http://mike.pirnat.com @mpirnat David Stanek http://traceback.org @dstanek