Chapter 29: IFrames

Attribute	Details
name	Sets the element’s name, to be used with an a tag to change the iframe’s src.
width	Sets the element’s width in pixels.
height	Sets the element’s height in pixels.
src	Specifies the page that will be displayed in the frame.
srcdoc	Specifies the content that will be displayed in the frame, assuming the browser supports it. The content must be valid HTML.
sandbox	When set, the contents of the iframe is treated as being from a unique origin and features including scripts, plugins, forms and popups will be disabled. Restrictions can be selectively relaxed by adding a space separated list of values. See the table in Remarks for possible values.
allowfullscreen	Whether to allow the iframe’s contents to use requestFullscreen( )

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.

<iframe src="base.html"></iframe>

Sandboxing

The following embeds an untrusted web page with all restrictions enabled

<iframe sandbox src="http://example.com/"></iframe>

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

<iframe sandbox="allow-scripts allow-forms" src="http://example.com/"></iframe>

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 it’s content using JavaScript.

<iframe sandbox="allow-same-origin allow-top-navigation"
src="http://example.com/untrusted/comments/page2">

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

<iframe src="base.html" width="800" height="600"></iframe>

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!”

<iframe srcdoc="<p>IFrames are cool!</p>"></iframe>

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.

<iframe srcdoc="<p>Iframes are cool!</p>" src="base.html"></iframe>

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.

<iframe src="webpage.html" name="myIframe"></iframe>
<a href="different_webpage.html" target="myIframe">Change the Iframe content to
different_webpage.html</a>