Vulnerability Note VU#143297

Mozilla Firefox allows cross-domain iframe access via JavaScript

Overview

Mozilla Firefox allows cross-domain access to an iframe. This vulnerability could allow an attacker to interact with a web site in a different domain. The attacker could read content and cookies, capture keystrokes, and modify content.

I. Description

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

The Mozilla same origin policy says:

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.

II. Impact

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.

III. Solution

We are currently unaware of a practical solution to this problem.

Workarounds for users

• Disable JavaScript
• 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.

Workarounds for administrators

• 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.

Systems Affected

Vendor	Status	Date Updated
Mozilla	Vulnerable	8-Jun-2007

References

http://archives.neohapsis.com/archives/fulldisclosure/2007-06/0026.html
https://bugzilla.mozilla.org/show_bug.cgi?id=382686
http://www.w3schools.com/tags/tag_iframe.asp
http://www.w3.org/TR/html401/present/frames.html#h-16.5
https://addons.mozilla.org/en-US/firefox/addon/722
http://www.mozilla.org/projects/security/components/same-origin.html
http://www.cert.org/archive/pdf/cross_site_scripting.pdf
http://www.stopbadware.org/home/security#preventing
http://www.antiphishing.org/consumer_recs.html

Credit

This vulnerability was reported by Michal Zalewski on the Full-Disclosure mailing list.

This document was written by Ryan Giobbi.

Other Information

Date Public	06/04/2007
Date First Published	06/08/2007 01:28:14 PM
Date Last Updated	06/14/2007
CERT Advisory
CVE Name	CVE-2007-3089
Metric	8.51
Document Revision	23