The Tangled Web

Chapter 11. Life Outside Same-Origin Rules

The same-origin policy is the most important mechanism we have to keep hostile web applications at bay, but it’s also an imperfect one. Although it is meant to offer a robust degree of separation between any two different and clearly identifiable content sources, it often fails at this task.

To understand this disconnect, recall that contrary to what common sense may imply, the same-origin policy was never meant to be all-inclusive. Its initial focus, the DOM hierarchy (that is, just the document object exposed to JavaScript code) left many of the peripheral JavaScript features completely exposed to cross-domain manipulation, necessitating ad hoc fixes. For example, a few years after the inception of SOP, ...