CWE-1022: Use of Web Link to Untrusted Target with window.opener Access

Description

The web application produces links to untrusted external sites outside of its sphere of control, but it does not properly prevent the external site from modifying security-critical properties of the window.opener object, such as the location property.

When a user clicks a link to an external site ("target"), the target="_blank" attribute causes the target site's contents to be opened in a new window or tab, which runs in the same process as the original page. The window.opener object records information about the original page that offered the link. If an attacker can run script on the target page, then they could read or modify certain properties of the window.opener object, including the location property - even if the original and target site are not the same origin. An attacker can modify the location property to automatically redirect the user to a malicious site, e.g. as part of a phishing attack. Since this redirect happens in the original window/tab - which is not necessarily visible, since the browser is focusing the display on the new target page - the user might not notice any suspicious redirection.

Potential Impact

Confidentiality

Alter Execution Logic

Demonstrative Examples

In this example, the application opens a link in a named window/tab without taking precautions to prevent the called page from tampering with the calling page's location in the browser.

There are two ways that this weakness is commonly seen. The first is when the application generates an <a> tag is with target="_blank" to point to a target site:

Bad

<a href="http://attacker-site.example.com/useful-page.html" target="_blank">

If the attacker offers a useful page on this link (or compromises a trusted, popular site), then a user may click on this link.  However, the attacker could use scripting code to modify the window.opener's location property to redirect the application to a malicious, attacker-controlled page - such as one that mimics the look and feel of the original application and convinces the user to re-enter authentication credentials, i.e. phishing:

Attack

window.opener.location = 'http://phishing.example.org/popular-bank-page';

To mitigate this type of weakness, some browsers support the "rel" attribute with a value of "noopener", which sets the window.opener object equal to null. Another option is to use the "rel" attribute with a value of "noreferrer", which in essence does the same thing.

Good

<a href="http://attacker-site.example.com/useful-page.html" target="_blank" rel="noopener noreferrer">

A second way that this weakness is commonly seen is when opening a new site directly within JavaScript. In this case, a new site is opened using the window.open() function.

Bad

var newWindow = window.open("http://attacker-site.example.com/useful-page.html", "_blank");

To mitigate this, set the window.opener object to null.

Good

var newWindow = window.open("http://attacker-site.example.com/useful-page.html", "_blank");newWindow.opener = null;

Mitigations & Prevention

Architecture and Design

Specify in the design that any linked external document must not be granted access to the location object of the calling page.

Implementation

When creating a link to an external document using the <a> tag with a defined target, for example "_blank" or a named frame, provide the rel attribute with a value "noopener noreferrer". If opening the external document in a new window via javascript, then reset the opener by setting it equal to null.

Implementation

Do not use "_blank" targets. However, this can affect the usability of the application.

Detection Methods

Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Real-World CVE Examples

CVE ID	Description
CVE-2022-4927	Library software does not use rel: "noopener noreferrer" setting, allowing tabnabbing attacks to redirect to a malicious page

Frequently Asked Questions

What is CWE-1022?

CWE-1022 (Use of Web Link to Untrusted Target with window.opener Access) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The web application produces links to untrusted external sites outside of its sphere of control, but it does not properly prevent the external site from modifying security-critical properties of the w...

How can CWE-1022 be exploited?

Attackers can exploit CWE-1022 (Use of Web Link to Untrusted Target with window.opener Access) to alter execution logic. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.

How do I prevent CWE-1022?

Key mitigations include: Specify in the design that any linked external document must not be granted access to the location object of the calling page.

What is the severity of CWE-1022?

CWE-1022 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 1 real-world CVEs.