How does a Embedding Scripts within Scripts attack work?

It typically unfolds over 5 phases. It begins with: [Spider] Using a browser or an automated tool, an adversary records all entry points for inputs that happen to be reflected in a client-side script element. These script elements can be located in the HTML content (head, body, comments), in an HTML tag, XML, CSS, etc.

How do you prevent CAPEC-19?

Use browser technologies that do not allow client side scripting.

What weaknesses does CAPEC-19 target?

CAPEC-19 exploits 1 CWE weakness, including CWE-284 (Improper Access Control).

How severe is CAPEC-19?

MITRE rates CAPEC-19 as High severity with high likelihood of attack.

CAPEC-19: Embedding Scripts within Scripts

An adversary leverages the capability to execute their own script by embedding it within other scripts that the target software is likely to execute due to programs' vulnerabilities that are brought on by allowing remote hosts to execute scripts.

Last updated June 1, 2026

High

Typical severity

Per MITRE

High

Likelihood of attack

Per MITRE

Related weaknesses

CWEs this targets

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Abstraction

MITRE classification

Overview

The adversary must have the ability to inject their script into a script that is likely to be executed. If this is done, then the adversary 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. 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 adversary can inject malicious scripts. Since this attack pattern defines scripts within scripts, there are likely privileges to execute said attack on the host. 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.

How the attack works

The phases an attacker typically follows to carry out this attack.

Step 1
Explore
[Spider] Using a browser or an automated tool, an adversary records all entry points for inputs that happen to be reflected in a client-side script element. These script elements can be located in the HTML content (head, body, comments), in an HTML tag, XML, CSS, etc.
- Use a spidering tool to follow and record all non-static links that are likely to have input parameters (through forms, URL, fragments, etc.) actively used by the Web application.
- Use a proxy tool to record all links visited during a manual traversal of the web application.
- Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery.
Step 2
Experiment

Examples

Ajax applications enable rich functionality for browser based web applications. Applications like Google Maps deliver unprecedented ability to zoom in and out, scroll graphics, and change graphic presentation through Ajax. The security issues that an adversary may exploit in this instance are the relative lack of security features in JavaScript and the various browser's implementation of JavaScript, these security gaps are what XSS and a host of other client side vulnerabilities are based on. While Ajax may not open up new security holes, per se, due to the conversational aspects between client and server of Ajax communication, attacks can be optimized. A single zoom in or zoom out on a graphic in an Ajax application may round trip to the server dozens of times. One of the first steps many adversarys take is frequently footprinting an environment, this can include scanning local addresses like 192.*.*.* IP addresses, checking local directories, files, and settings for known vulnerabilities, and so on. The XSS script that is embedded in a given IMG tag can be manipulated to probe a different address on every click of the mouse or other motions that the Ajax application is aware of. In addition the enumerations allow for the adversary to nest sequential logic in the attacks. While Ajax applications do not open up brand new attack vectors, the existing attack vectors are more than adequate to execute attacks, and now these attacks can be optimized to sequentially execute and enumerate host environments.

~/.bash_profile and ~/.bashrc are executed in a user's context when a new shell opens or when a user logs in so that their environment is set correctly. ~/.bash_profile is executed for login shells and ~/.bashrc is executed for interactive non-login shells. This means that when a user logs in (via username and password) to the console (either locally or remotely via something like SSH), ~/.bash_profile is executed before the initial command prompt is returned to the user. After that, every time a new shell is opened, ~/.bashrc is executed. This allows users more fine grained control over when they want certain commands executed. These files are meant to be written to by the local user to configure their own environment; however, adversaries can also insert code into these files to gain persistence each time a user logs in or opens a new shell.

CAPEC-19: Embedding Scripts within Scripts

Overview

How the attack works

What the attacker needs

Prerequisites

Skills required

Consequences

How to mitigate it

Examples

Terminology & mappings

Mapped taxonomies

Frequently asked questions

References

Defend against CAPEC-19

Overview

How the attack works

What the attacker needs

Prerequisites

Skills required

Consequences

How to mitigate it

Examples

Related weaknesses

Related attack patterns

Parent

Terminology & mappings

Mapped taxonomies

Frequently asked questions

References

Defend against CAPEC-19