HTML IFrames

Basics of an Inline Frame

The term "IFrame" means Inline Frame. It can be used to include another page in your page. This will yield a small frame which shows the exact contents of the base.html.

Sandboxing

The following embeds an untrusted web page with all restrictions enabled

To allow the page to run scripts and submit forms, add allow-scripts and allow-forms to the sandbox attribute.

If there is untrusted content (such as user comments) on the same domain as the parent web page, an iframe can be used to disable scripts while still allowing the parent document to interact with its content using JavaScript.

The parent document can add event listeners and resize the IFrame to fit its contents. This, along with allow-top navigation, can make the sandboxed iframe appear to be part of the parent document.

This sandbox is not a replacement for sanitizing input but can be used as part of a defense in depth strategy. Also be aware that this sandbox can be subverted by an attacker convincing a user to visit the iframe's source directly. The Content Security Policy HTTP header can be used to mitigate this attack.

Setting the Frame Size

The IFrame can be resized using the width and height attributes, where the values are represented in pixels (HTML 4.01 allowed percentage values, but HTML 5 only allows values in CSS pixels).

Using the "srcdoc" Attribute

The srcdoc attribute can be used (instead of the src attribute) to specify the exact contents of the iframe as a whole HTML document. This will yield an IFrame with the text "IFrames are cool!"

If the srcdoc attribute isn't supported by the browser, the IFrame will instead fall back to using the src attribute, but if both the src and srcdoc attributes are present and supported by the browser, srcdoc takes precedence.

In the above example, if the browser does not support the srcdoc attribute, it will instead display the contents of the base.html page.

Using Anchors with IFrames

Normally a change of webpage within an Iframe is initiated from with the Iframe, for example, clicking a link inside the Ifame. However, it is possible to change an IFrame's content from outside the IFrame. You can use an anchor tag whose href attribute is set to the desired URL and whose target attribute is set to the iframe's name attribute.