# Reverse Tab Nabbing

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## Description

In a situation where an **attacker** can **control** the **`href`** argument of an **`<a`** tag with the attribute **`target="_blank" rel="opener"`** that is going to be clicked by a victim, the **attacker** **point** this **link** to a web under his control (a **malicious** **website**). Then, once the **victim clicks** the link and access the attackers website, this **malicious** **website** will be able to **control** the **original** **page** via the javascript object **`window.opener`**.\
If the page doesn't have **`rel="opener"` but contains `target="_blank"` it also doesn't have `rel="noopener"`** it might be also vulnerable.

A regular way to abuse this behaviour would be to **change the location of the original web** via `window.opener.location = https://attacker.com/victim.html` to a web controlled by the attacker that **looks like the original one**, so it can **imitate** the **login** **form** of the original website and ask for credentials to the user.

However, note that as the **attacker now can control the window object of the original website** he can abuse it in other ways to perform **stealthier attacks** (maybe modifying javascript events to ex-filtrate info to a server controlled by him?)

## Overview

### With back link

Link between parent and child pages when prevention attribute is not used:

![https://owasp.org/www-community/assets/images/TABNABBING\_OVERVIEW\_WITH\_LINK.png](https://owasp.org/www-community/assets/images/TABNABBING_OVERVIEW_WITH_LINK.png)

### Without back link

Link between parent and child pages when prevention attribute is used:

![https://owasp.org/www-community/assets/images/TABNABBING\_OVERVIEW\_WITHOUT\_LINK.png](https://owasp.org/www-community/assets/images/TABNABBING_OVERVIEW_WITHOUT_LINK.png)

### Examples <a href="#examples" id="examples"></a>

Create the following pages in a folder and run a web server with `python3 -m http.server`\
Then, **access** `http://127.0.0.1:8000/`vulnerable.html, **click** on the link and note how the **original** **website** **URL** **changes**.

{% code title="vulnerable.html" %}

```markup
<!DOCTYPE html>
<html>
<body>
<h1>Victim Site</h1>
<a href="http://127.0.0.1:8000/malicious.html" target="_blank" rel="opener">Controlled by the attacker</a>
</body>
</html>
```

{% endcode %}

{% code title="malicious.html" %}

```markup
<!DOCTYPE html>
<html>
 <body>
  <script>
  window.opener.location = "http://127.0.0.1:8000/malicious_redir.html";
  </script>
 </body>
</html>
```

{% endcode %}

{% code title="malicious\_redir.html" %}

```markup
<!DOCTYPE html>
<html>
<body>
<h1>New Malicious Site</h1>
</body>
</html>
```

{% endcode %}

### Accessible properties <a href="#accessible-properties" id="accessible-properties"></a>

In the scenario where a **cross-origin** access occurs (access across different domains), the properties of the **window** JavaScript class instance, referred to by the **opener** JavaScript object reference, that can be accessed by a malicious site are limited to the following:

* **`opener.closed`**: This property is accessed to determine if a window has been closed, returning a boolean value.
* **`opener.frames`**: This property provides access to all iframe elements within the current window.
* **`opener.length`**: The number of iframe elements present in the current window is returned by this property.
* **`opener.opener`**: A reference to the window that opened the current window can be obtained through this property.
* **`opener.parent`**: This property returns the parent window of the current window.
* **`opener.self`**: Access to the current window itself is provided by this property.
* **`opener.top`**: This property returns the topmost browser window.

However, in instances where the domains are identical, the malicious site gains access to all properties exposed by the [**window**](https://developer.mozilla.org/en-US/docs/Web/API/Window) JavaScript object reference.

## Prevention

Prevention information are documented into the [HTML5 Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/HTML5_Security_Cheat_Sheet.html#tabnabbing).

### References

* <https://owasp.org/www-community/attacks/Reverse_Tabnabbing>

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<summary>Support HackTricks</summary>

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{% endhint %}
