Of course, these attacks are not solely limited to the server side, client side scripts like Ajax and client side JavaScript can contain malicious scripts as well. Since this attack pattern defines scripts within scripts, there are likely privileges to execute said attack on the host. With the proliferation of intermediaries, such as Web App Firewalls, network devices, and even printers having JVMs and Web servers, there are many locales where an attacker can inject malicious scripts.
If this is done, then the attacker can potentially launch a variety of probes and attacks against the web server's local environment, in many cases the so-called DMZ, back end resources the web server can communicate with, and other hosts. The attacker must have the ability to inject script into script that is likely to be executed.
The attacker leverages this capability to execute scripts to execute his/her own script by embedding it within other scripts that the target software is likely to execute. An attack of this type exploits a programs' vulnerabilities that are brought on by allowing remote hosts to execute scripts.