# Lab 2: DOM XSS via client-side prototype pollution

Primero ejecutamos lo siguiente:

<figure><img src="/files/fjf7y5S1eGLf6IWOg5om" alt=""><figcaption></figcaption></figure>

Y luego modificamos la URL:

<figure><img src="/files/8gpypSoDRs0WroekGdxI" alt=""><figcaption></figcaption></figure>

Se puede apreciar el retorno de `foo:bar`

Así que procedemos analizar el código fuente:

<figure><img src="/files/mHjmaJ6Bq5KGV9nuV9rB" alt=""><figcaption></figcaption></figure>

La linea susceptible a prototype:

```
let config = {params: deparam(new URL(location).searchParams.toString())};
```

Y por lo anterior, se procede a utilizar la siguiente carga:&#x20;

```
?__proto__[transport_url]=foo
```

<figure><img src="/files/yPJSjk0j6v6rYqgghgro" alt=""><figcaption></figcaption></figure>

En la evidencia previa, se puede apreciar el src apuntando a foo.

Modificamos nuestro payload para obtener un XSS:

<figure><img src="/files/kbSMIgdQym7W7jYiUn24" alt=""><figcaption></figcaption></figure>


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