CAPEC-86 XSS Through HTTP Headers – Attack Pattern Analysis

CAPEC-86 Metadata

Likelihood of Attack

High

Typical Severity

Very High

Overview

Summary

An adversary exploits web applications that generate web content, such as links in a HTML page, based on unvalidated or improperly validated data submitted by other actors. XSS in HTTP Headers attacks target the HTTP headers which are hidden from most users and may not be validated by web applications.

Prerequisites

Target software must be a client that allows scripting communication from remote hosts.

Execution Flow

Step	Phase	Description	Techniques
1	Explore	[Survey the application for public links] Using a browser or an automated tool, an adversary follows all public links on a web site. They record all the entry points (input) that becomes part of generated HTTP header (not only GET/POST/COOKIE, but also Content-Type, etc.)	Use a spidering tool to follow and record all links and analyze the web pages to find entry points. Make special note of any links that include parameters used in the HTTP headers. Look for HTML meta tags that could be injectable 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.
2	Experiment	[Probe identified potential entry points for XSS vulnerability]The adversary uses the entry points gathered in the "Explore" phase as a target list and injects various common script payloads to determine if an entry point actually represents a vulnerability and to characterize the extent to which the vulnerability can be exploited. They record all the responses from the server that include unmodified versions of their script. The adversary tries also to inject extra-parameter to the HTTP request to see if they are reflected back in the web page or in the HTTP response.	Manually inject various script payloads into each identified entry point using a list of common script injection probes and observe system behavior to determine if script was executed. Use an automated injection attack tool to inject various script payloads into each identified entry point using a list of common script injection probes and observe system behavior to determine if script was executed. Use a proxy tool to record results of manual input of XSS probes in known URLs.
3	Experiment	[Craft malicious XSS URL] Once the adversary has determined which parameters are vulnerable to XSS, they will craft a malicious URL containing the XSS exploit. The adversary can have many goals, from stealing session IDs, cookies, credentials, and page content from the victim.	Change a URL parameter which is used in an HTTP header to include a malicious script tag. Because it is in the header it may bypass validation. Send information gathered from the malicious script to a remote endpoint.
4	Exploit	[Get victim to click URL] In order for the attack to be successful, the victim needs to access the malicious URL.	Send a phishing email to the victim containing the malicious URL. This can be hidden in a hyperlink as to not show the full URL, which might draw suspicion. Put the malicious URL on a public forum, where many victims might accidentally click the link.

Potential Solutions / Mitigations

Design: Use browser technologies that do not allow client side scripting. Design: Utilize strict type, character, and encoding enforcement Design: 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. Implementation: Ensure all content that is delivered to client is sanitized against an acceptable content specification. Implementation: Perform input validation for all remote content. Implementation: Perform output validation for all remote content. Implementation: Disable scripting languages such as JavaScript in browser Implementation: Session tokens for specific host Implementation: 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.

Related Weaknesses (CWE)

CWE ID	Description
CWE-80	Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

Related CAPECs

CAPEC ID	Description
CAPEC-588	This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is inserted into the client-side HTML being parsed by a web browser. Content served by a vulnerable web application includes script code used to manipulate the Document Object Model (DOM). This script code either does not properly validate input, or does not perform proper output encoding, thus creating an opportunity for an adversary to inject a malicious script launch a XSS attack. A key distinction between other XSS attacks and DOM-based attacks is that in other XSS attacks, the malicious script runs when the vulnerable web page is initially loaded, while a DOM-based attack executes sometime after the page loads. Another distinction of DOM-based attacks is that in some cases, the malicious script is never sent to the vulnerable web server at all. An attack like this is guaranteed to bypass any server-side filtering attempts to protect users.
CAPEC-591	This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is "reflected" off a vulnerable web application and then executed by a victim's browser. The process starts with an adversary delivering a malicious script to a victim and convincing the victim to send the script to the vulnerable web application.
CAPEC-592	An adversary utilizes a form of Cross-site Scripting (XSS) where a malicious script is persistently "stored" within the data storage of a vulnerable web application as valid input.