All Laravel components are available from here https://github.com/illuminate.
All components are installable throught Composer, but none of them are very well documentent unfornunally.
Laravel does use many Symfony components which are actually very well documented.
But i would imagine that you're interested in the Illuminate\Http component and specifically the Illuminate\Http\Request class, which is just an extension of the Symfony\Component\HttpFoundation\Request with some sugar added to it.
But Neither the Illuminate\Http\Request or the Symfony\Component\HttpFoundation\Request class does any sanitizing.
But if you want to, you could use the Illuminate\Http\Request class and extends it's input method and add sanitization to the value before it's returned?
The Illuminate\Http\Request class is quite simple to bootstrap in you application:
$request = Illuminate\Http\Request::capture();
from here on, you can use the $request->input($key) method to recive a post- or query value.
Hope that pointed you in some direction :)