Securing frame communication in browsers

Many web sites embed third-party content in frames, relying on the browser's security policy to protect them from malicious content. Frames, however, are often insufficient isolation primitives because most browsers let framed content manipulate other frames through navigation. We evaluate existing frame navigation policies and advocate a stricter policy, which we deploy in the open-source browsers. In addition to preventing undesirable interactions, the browser's strict isolation policy also hinders communication between cooperating frames. We analyze two techniques for inter-frame communication. The first method, fragment identifier messaging, provides confidentiality without authentication, which we repair using concepts from a well-known network protocol. The second method, postMessage, provides authentication, but we discover an attack that breaches confidentiality. We modify the postMessage API to provide confidentiality and see our modifications standardized and adopted in browser implementations.