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Use of Web Link to Untrusted Target with window.opener Access

Incomplete Variant
Structure: Simple
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.

Extended Description

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.
Common Consequences 1
Scope: Confidentiality

Impact: Alter Execution Logic

The user may be redirected to an untrusted page that contains undesired content or malicious script code.
Detection Methods 1
Automated Static AnalysisHigh
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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Potential Mitigations 3
Phase: 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.
Phase: 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.
Phase: Implementation
Do not use "_blank" targets. However, this can affect the usability of the application.
Demonstrative Examples 1
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:

Code Example:

Bad
HTML
html
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:

Code Example:

Attack
JavaScript
javascript
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.

Code Example:

Good
HTML
html
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.

Code Example:

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

Code Example:

Good
JavaScript
javascript
Observed Examples 1
CVE-2022-4927Library software does not use rel: "noopener noreferrer" setting, allowing tabnabbing attacks to redirect to a malicious page
References 3
Target="_blank" - the most underestimated vulnerability ever
Alex Yumashev
04-05-2016
https://medium.com/@jitbit/target-blank-the-most-underestimated-vulnerability-ever-96e328301f4c
ID: REF-39
The target="_blank" vulnerability by example
Ben Halpern
11-09-2016
https://dev.to/ben/the-targetblank-vulnerability-by-example
ID: REF-40
About rel=noopener
Mathias Bynens
15-03-2016
https://mathiasbynens.github.io/rel-noopener/
ID: REF-958
Likelihood of Exploit

Medium

Applicable Platforms
Languages:
JavaScript : Often
Technologies:
Web Based : Often
Modes of Introduction
Architecture and Design
Implementation
Alternate Terms

tabnabbing
Related Weaknesses
ChildOf: Incorrect Privilege Assignment (CWE-266)