CAPEC-86: XSS Through HTTP Headers
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.
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Overview
CAPEC-86 (XSS Through HTTP Headers) is a detailed-level attack pattern catalogued by MITRE in the Common Attack Pattern Enumeration and Classification (CAPEC). It describes a recurring method attackers use to exploit software weaknesses.
How the attack works
The phases an attacker typically follows to carry out this attack.
- Step 1Explore
[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.
- Step 2Experiment
[Probe identified potential entry points for XSS vulnerability]
- 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.
- Step 3Experiment
[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.
- Step 4Exploit
[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.
What the attacker needs
Prerequisites
- Target software must be a client that allows scripting communication from remote hosts.
Skills required
- Low skill: To achieve a redirection and use of less trusted source, an adversary can simply edit HTTP Headers that are sent to client machine.
- High skill: Exploiting a client side vulnerability to inject malicious scripts into the browser's executable process.
Resources required
- The adversary must have the ability to deploy a custom hostile service for access by targeted clients and the abbility to communicate synchronously or asynchronously with client machine. The adversary must also control a remote site of some sort to redirect client and data to.
Consequences
What a successful CAPEC-86 attack can achieve.
Execute Unauthorized Commands
Affects: Confidentiality, Integrity, Availability
Run Arbitrary Code
Read Data
Affects: Confidentiality
Gain Privileges
Affects: Confidentiality, Access Control, Authorization
How to mitigate it
Defenses that reduce the risk of CAPEC-86.
- 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.
Examples
Utilize a remote style sheet set in the HTTP header for XSS attack. When the adversary is able to point to a remote stylesheet, any of the variables set in that stylesheet are controllable on the client side by the remote adversary. Like most XSS attacks, results vary depending on browser that is used [REF-97]. ; REL=stylesheet">
Google's 404 redirection script was found vulnerable to this attack vector. Google's 404 file not found page read * Response headers: "Content-Type: text/html; charset=[encoding]". * Response body: If the response sends an unexpected encoding type such as UTF-7, then no enforcement is done on the payload and arbitrary XSS code will be transported along with the standard HTTP response. [REF-476]
XSS can be used in variety of ways, because it is scripted and executes in a distributed, asynchronous fashion it can create its own vector and openings. For example, the adversary can use XSS to mount a DDoS attack by having series of different computers unknowingly executing requests against a single host.
Frequently asked questions
Common questions about CAPEC-86.
- What is CAPEC-86?
- 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.
- How does a XSS Through HTTP Headers attack work?
- It typically unfolds over 4 phases. It begins with: [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.)
- How do you prevent CAPEC-86?
- Design: Use browser technologies that do not allow client side scripting.
- What weaknesses does CAPEC-86 target?
- CAPEC-86 exploits 1 CWE weakness, including CWE-80 (Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)).
- How severe is CAPEC-86?
- MITRE rates CAPEC-86 as Very High severity with high likelihood of attack.
References
Attack-pattern data is sourced from the MITRE CAPEC catalog (v3.9). Weakness associations link to the corresponding CWE entries on RadicalNotion.AI.
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