A web application decomposed into one or more domain sandboxes ensures that the contents of each sandbox are protected from attacks on the web application outside that sandbox. Sandboxing is achieved on a per-element basis by identifying content that should be put under protection, generating a secure domain name for the identified content, and replacing the identified content with a unique reference (e.g., an iframe) to the generated secure domain. The identified content is then served only from the generated secure domain using a content handler.