Session-only cookie corruption in Ruby web apps

Rack and Rails have a cookie monster.

Browsers place limits on the number and size of cookies present for a domain or in a response. If you exceed these limits, Bad Things can happen. Rack and Rails try to prevent this in the obvious cases, but this post describes what they get wrong in their current implementations. We’ll also review the potential impact of—and how you can mitigate—this type of issue in your Ruby web apps.

This information is most relevant for web apps that transmit session cookies that contain the encoded contents of the entire session hash—not just the session ID. In other words, a cookie-only session. For example, Rack::Session::Cookie with Marshal or JSON, Rails’ default ActionDispatch::Session::CookieStore, or an implementation of JWT (JSON Web Tokens) that uses a cookie (instead of a dedicated response header) as its transport. The security risks are greatest when cookie-only sessions meet the cookie-truncation behavior of older browsers (and can be compounded when the sessions contain arbitrarily-large data, such as flash messages).

TL;DR: If your Ruby web apps use cookie-only sessions, consider adding Rack::Protection::MaximumCookie to their middleware stacks.

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How fanriff.com works, Part I

I thought I’d write about how fanriff.com serves its Ember.js index from its Sinatra.rb API, and how web clients interacts with the back-end once the application is loaded. It started to run a little long so I’ve broken it up into parts. This first chapter will cover some background information on Ember, the fanriff.com web architecture, and how we deploy our Ember index to our stack.

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Web site security checklists

There are a tremendous number of things you can do today to make your site more secure, while preserving compatibility with all but the oldest web clients (I’m looking at you, Java 6 and Internet Explorer 6). If you haven’t been keeping up with the state of the art, this includes things like (cue Benny Hill music):

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