Software Engineering Institute

An iframe is an HTML element which allows an HTML document to be embedded inside a master HTML document.

The Mozilla same origin policy states:
The same origin policy prevents document or script loaded from one origin from getting or setting properties of a document from a different origin. The policy dates from Netscape Navigator 2.0.

Mozilla considers two pages to have the same origin if the protocol, port (if given), and host are the same for both pages.
Firefox does not properly enforce the same origin policy to web pages that use iframes.

From Mozilla Bugzilla Bug ID 382686:

The problem you fixed there is that document.write() could be used to overwrite frames that originate from Internet-based SRC= pointing to non-same-domain site. This is fixed and throws a security exception.

Unfortunately, the check implemented means that about:blank frames can be overwritten freely; and unfortunately, *all* frames, even with Internet SRC= specified, will be vulnerable to a race condition while the document loads.
Note that some websites that allow users to supply content may allow iframes to be included.

An attacker may be able to obtain sensitive data from a user, modify the appearance of a webpage or track keystrokes. Depending on the nature of the web site the user was visiting, this data may include passwords, credit card numbers, and any arbitrary information provided by the user.

Mozilla has addressed this issue with Firefox 2.0.0.5. Please see Mozilla Foundation Security Advisory 2007-20 for details.

Workarounds for users

• Disable JavaScript (see Securing Your Web Browser).
• Use the NoScript Firefox Add-on to whitelist what sites can run JavaScript.
• Type in URLs directly in the web browser's address bar, or use bookmarks to navigate to websites.
• See the Cross-Site Scripting Vulnerabilities document for general information.

• Do not allow user submitted content to include JavaScript.
• Do not allow users to submit content to a shared resource that includes iframes. A shared resource may include the comments section of a blog or a web forum.
• Monitor the content submitted by third parties for malicious JavaScript or iframes.