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CAPEC-464: Evercookie

Definition in a New Window Definition in a New Window
Attack Pattern ID: 464
Abstraction: Standard
Status: Draft
Completeness: Stub
Presentation Filter:
+ Summary

An attacker creates a very persistent cookie that stays present even after the user thinks it has been removed. The cookie is stored on the victim's machine in over ten places to include: Standard HTTP Cookies, Local Shared Objects (Flash Cookies), Silverlight Isolated Storage, Storing cookies in RGB values of auto-generated, force-cached, PNGs using HTML5 Canvas tag to read pixels (cookies) back out, Storing cookies in Web History, Storing cookies in HTTP ETags, Storing cookies in Web cache, window.name caching, Internet Explorer userData storage, HTML5 Session Storage, HTML5 Local Storage, HTML5 Global Storage, HTML5 Database Storage via SQLite, among others.

When the victim clears the cookie cache via traditional means inside the browser, that operation removes the cookie from certain places but not others. The malicious code then replicates the cookie from all of the places where it was not deleted to all of the possible storage locations once again. So the victim again has the cookie in all of the original storage locations. In other words, failure to delete the cookie in even one location will result in the cookie's resurrection everywhere. The evercookie will also persist across different browsers because certain stores (e.g., Local Shared Objects) are shared between different browsers.

+ Attack Prerequisites
  • The victim's browser is not configured to reject all cookies

    The victim visits a website that serves the attackers' evercookie

+ Typical Severity


+ Resources Required

Evercookie source code

+ Solutions and Mitigations

Design: Browser's design needs to be changed to limit where cookies can be stored on the client side and provide an option to clear these cookies in all places, as well as another option to stop these cookies from being written in the first place.

Design: Safari browser's private browsing mode is currently effective against evercookies.

+ References
[R.464.1] Samy Kamkar. "Evercookie". September 9, 2010. <http://samy.pl/evercookie/>.
+ Content History
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team
CAPEC Content TeamThe MITRE Corporation2015-12-07Updated Description Summary, Related_Attack_PatternsInternal

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Page Last Updated or Reviewed: August 04, 2017