# XSSI (Cross Site Script Inclusion) **Vulnerability: Cross Site Script Inclusion (XSSI)** #### Overview: XSSI, or Cross Site Script Inclusion, is a security vulnerability that facilitates the unauthorized leakage of sensitive data from one domain to another. This includes critical information like login credentials, tokens, cookies, session IDs, and personal user data such as mobile numbers, credit card information, emails, and addresses. #### Understanding XSSI: 1. **Same Origin Policy (SOP):** * SOP restricts websites from accessing data from domains other than their own. * Notably, HTML ` ``` * The injected code fetches sensitive data from `https://vulnsite.com/p/?showinfo=abc` and sends it to the attacker's server. 4. **Victim Interaction:** * The attacker delivers the URL `https://attacker.com/index.html` to an authenticated victim. * Victim data is fetched, and the attacker can monitor it on their log server. #### Remediation: 1. **Avoid Interpolating Sensitive Data:** * Refrain from interpolating sensitive data in JavaScript files. 2. **Use JSON URLs:** * Utilize JSON URLs instead of embedding sensitive data directly in JavaScript files. 3. **Avoid JSONP:** * Do not use JSONP, as it loads script elements and bypasses the Same Origin Policy. 4. **Content Type Consideration:** * Choose JSON or HTML content types, as they are subject to the browser's same-origin policy, preventing XSSI attacks. ## Reports {% embed url="" %} {% endembed %} {% embed url="" %} {% embed url="" %} {% embed url="" %} ## Writeups {% embed url="" %} {% embed url="" %} {% embed url="" %} {% endembed %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://sallam.gitbook.io/sec-88/web-appsec/xssi-cross-site-script-inclusion.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.