# Client Side Template Injection \(CSTI\)
## Summary
It is like a [**Server Side Template Injection**](ssti-server-side-template-injection.md) 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/)
### 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%28%27alert%28%22foo%22%29%27%29%28%29%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
```
### Mavo
Payload:
```text
[self.alert(1)]
```