CAPEC-19

Standard Abstraction Level
Meta — Very abstract, high-level category
Standard — Specific enough to understand
Detailed — Tied to specific technique Stable MITRE CAPEC Status
Stable — Fully reviewed and complete
Draft — Under development
Incomplete — Partially defined
Deprecated — No longer recommended
Obsolete — Replaced by another CAPEC Likelihood: High Severity: High
Embedding Scripts within Scripts

Description

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.

Prerequisites

Target software must be able to execute scripts, and also grant the adversary privilege to write/upload scripts.

Mitigations

Use browser technologies that do not allow client side scripting.

Utilize strict type, character, and encoding enforcement.

Server side developers should not proxy content via XHR or other means. If a HTTP proxy for remote content is setup on the server side, the client's browser has no way of discerning where the data is originating from.

Ensure all content that is delivered to client is sanitized against an acceptable content specification.

Perform input validation for all remote content.

Perform output validation for all remote content.

Disable scripting languages such as JavaScript in browser

Session tokens for specific host

Patching software. There are many attack vectors for XSS on the client side and the server side. Many vulnerabilities are fixed in service packs for browser, web servers, and plug in technologies, staying current on patch release that deal with XSS countermeasures mitigates this.

Privileges are constrained, if a script is loaded, ensure system runs in chroot jail or other limited authority mode

Skills Required

[Low] To load malicious script into open, e.g. world writable directory

[Medium] Executing remote scripts on host and collecting output