Twisted vulnerable to NameVirtualHost Host header injection
When the host header does not match a configured host, `twisted.web.vhost.NameVirtualHost` will return a `NoResource` resource which renders the Host header unescaped into the 404 response allowing HTML and script injection.
Example configuration:
```python
from twisted.web.server import Site
from twisted.web.vhost import NameVirtualHost
from twisted.internet import reactor
resource = NameVirtualHost()
site = Site(resource)
reactor.listenTCP(8080, site)
reactor.run()
```
Output:
```
❯ curl -H"Host:<h1>HELLO THERE</h1>"
http://localhost:8080/
<html>
<head><title>404 - No Such Resource</title></head>
<body>
<h1>No Such Resource</h1>
<p>host b'<h1>hello there</h1>' not in vhost map</p>
</body>
</html>
```
This vulnerability was introduced in f49041bb67792506d85aeda9cf6157e92f8048f4 and first appeared in the 0.9.4 release.