OWASP AppSec USA 2017: Cookie Security – Myths and Misconceptions by David Johansson
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1. The document discusses various myths and misconceptions around cookie security, focusing on the 'Secure', 'HttpOnly', 'Path', and 'Domain' cookie attributes. 2. While attributes like 'Secure' and 'HttpOnly' provide some protections, they have limitations and weaknesses that can be exploited. For example, 'Secure' only protects confidentiality, not integrity, while 'HttpOnly' can be bypassed through JavaScript. 3. The document recommends using the strictest cookie settings possible, like limiting the cookie domain and path, using short expiration times, and taking advantage of new protections in RFC6265bis such as 'SameSite' and cookie prefixes.
![The ‘SameSite’ Attribute
• Problem:
– Cookies are sent with all requests to a server, regardless of request
origin
– Attackers can abuse this by initiating authenticated cross-origin
requests, e.g., CSRF, XSSI, etc.
• Solution:
– New cookie attribute SameSite=[Strict|Lax]
– Prevents cookies from being attached to cross-origin requests](https://image.slidesharecdn.com/appsecusa2017davidjohansson-cookiesecuritymythsandmisconcepti-171002212453/85/OWASP-AppSec-USA-2017-Cookie-Security-Myths-and-Misconceptions-by-David-Johansson-29-320.jpg)
OWASP AppSec USA 2017: Cookie Security – Myths and Misconceptions by David Johansson
- 1. Cookie Security Myths and Misconceptions David Johansson - AppSec USA 2017
- 2. About Me • David Johansson (@securitybits) – Security consultant with 10 years in AppSec – Helping clients design and build secure software – Develop and deliver security training – Based in London, working for Synopsys
- 3. Cookie Security • Why talk about Cookie Security? Cookie security is somewhat broken… Image src: https://commons.wikimedia.org/wiki/File:Choco_chip_cookie_half.png (Author: Bob Smith, modifications made by Chzz)
- 4. Agenda • Cookie Basics • The ‘Secure’ Attribute • The ‘HttpOnly’ Attribute • The ‘Path’ Attribute • The ‘Domain’ Attribute • Cookie Lifetime • Modern Cookie Protections • Summary
- 6. History of HTTP Cookies Cookies are based on an old recipe: • 1994 –Netscape draft • 1997 – RFC 2109 • 2000 – RFC 2965 • 2002 – HttpOnly • 2011 – RFC 6265 • 2017 – RFC 6265bis (draft) “Classic Film” (https://www.flickr.com/photos/29069717@N02/)
- 7. HTTP Cookies • Cookies are sent in HTTP headers • Attributes influence how cookies are managed by the client (e.g., browser) Server response HTTP/1.1 200 OK … Set-Cookie: id=2bf353246gf3; Secure; HttpOnly Set-Cookie: lang=en; Expires=Wed, 09 Jun 2021 10:18:14 GMT Subsequent client request GET /index.html HTTP/1.1 … Cookie: id=2bf353246gf3; lang=en
- 8. THE ‘SECURE’ ATTRIBUTE Keeping Cookies Secure from Network-level Attackers
- 9. The ‘Secure’ Attribute “Cookies marked with the ‘Secure’ attribute are only sent over encrypted HTTPS connections and are therefore safe from man- in-the-middle attacks.” –True or false?
- 10. The ‘Secure’ Attribute • The ‘Secure’ attribute only protects the confidentiality of a cookie against MiTM attackers – there is no integrity protection! – Mallory can’t read ‘secure’ cookies – Mallory can still write/change ‘secure’ cookies Image source: https://commons.wikimedia.org/wiki/File:Man_in_the_middle_attack.svg (Author: Miraceti, No changes made, Creative Commons Attribution-Share Alike 3.0 Unported)
- 11. DEMO Bypassing the ‘Double-submit Cookie Pattern’ CSRF Defense
- 12. THE ‘HTTPONLY’ ATTRIBUTE Keeping JavaScript’s Hands Away from the Cookie Jar
- 13. The ‘HttpOnly’ Attribute “Cookies marked with the ‘HttpOnly’ attribute are not accessible from JavaScript and therefore unaffected by cross-site scripting (XSS) attacks.” –True or false?
- 14. The ‘HttpOnly’ Attribute Picture by Greg Putrich (flickr.com) • Only confidentiality protected in practice • HttpOnly-cookies can be replaced by overflowing the cookie jar from JavaScript Image src: https://www.flickr.com/photos/migrashgrutot/6905482601/in/photolist-bwdpoR (Author: Greg Putrich, No Modifications, https://creativecommons.org/licenses/by-nc-nd/2.0/)
- 15. DEMO Overwriting a Cookie Marked as ‘HttpOnly’ from JavaScript
- 16. THE ‘PATH’ ATTRIBUTE Isolating Cookies to Specific Paths
- 17. The ‘Path’ Attribute “The ‘Path’ attribute limits the scope of a cookie to a specific path on the server and can therefore be used to prevent unauthorized access to it from other applications on the same host.” –True or false?
- 18. The ‘Path’ Attribute • Cookie Scope vs. Same-origin Policy Host/domainPath Port & Protocol Cookie Scope Same-origin Policy
- 19. The ‘Path’ Attribute example .com /App1 https (443) Isolated in terms of cookie scope Not isolated in terms of SOP! /App2 • Two different applications on shared host: – https://example.com/App1/ – https://example.com/App2/
- 20. THE ‘DOMAIN’ ATTRIBUTE Only Send Cookie to Intended Host(s)
- 21. The ‘Domain’ Attribute “The ‘Domain’ attribute should be set to the origin host to limit the scope to that particular server. For example if the application resides on server app.mysite.com, then it should be set to domain=app.mysite.com” –True or false?
- 22. The ‘Domain’ Attribute • When domain set, cookies will be sent to that domain and all its subdomains • The risk with subdomains is lower than when scoped to parent domain, but still relevant • Remove domain attribute to limit cookie to origin host only – Important note: IE will always send to subdomains regardless
- 23. COOKIE LIFETIME Limiting Exposure of Cookies
- 24. Cookie Lifetime “A session cookie, also known as an in-memory cookie or transient cookie, exists only in temporary memory while the user navigates the website.” (Wikipedia) –True or false?
- 25. Cookie Lifetime • It’s up to the browser to decide when the session ends • ‘Non-persistent’ session cookies may actually be persisted to survive browser restart https://developer.mozilla.org/en-US/docs/Web/API/document/cookie
- 26. MODERN COOKIE PROTECTIONS RFC6265bis: Making Improvements to the Cookie Recipe
- 27. Strict Secure Cookies • Makes ‘secure’ cookies a little more secure by adding integrity protection • Prevents plain-text HTTP responses from setting or overwriting ‘secure’ cookies • Attackers still have a window of opportunity to “pre-empt” secure cookies with their own
- 28. Cookie Prefixes • Problem: – Server only sees cookie name and value in HTTP request, no information about its attributes – Impossible for server to know if a cookie it receives was set securely • Solution: – ‘Smuggle’ information to server in cookie name – "__Secure-" prefix – "__Host-" prefix
- 29. The ‘SameSite’ Attribute • Problem: – Cookies are sent with all requests to a server, regardless of request origin – Attackers can abuse this by initiating authenticated cross-origin requests, e.g., CSRF, XSSI, etc. • Solution: – New cookie attribute SameSite=[Strict|Lax] – Prevents cookies from being attached to cross-origin requests
- 30. SUMMARY
- 31. Summary • Key Takeaways: – Cookies are still largely based on a draft from 1994 – The security model has many weaknesses – Don’t build your application on false assumptions about cookie security – Application and framework developers should take advantage of new improvements to cookie security – Beware that not all browsers are using the same cookie recipe (yet)
- 32. The ‘Ultimate’ Cookie • Is there an ‘ultimate’ cookie configuration? • This is probably the most secure configuration we have for now: Set-Cookie: __Host-SessionID=3h93…; Path=/;Secure;HttpOnly;SameSite=Strict