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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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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.
The phases an attacker typically follows to carry out this attack.
[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.)
[Probe identified potential entry points for XSS vulnerability]
[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.
[Get victim to click URL] In order for the attack to be successful, the victim needs to access the malicious URL.
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
Defenses that reduce the risk of CAPEC-86.
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.
Common questions about 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.
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.)
Design: Use browser technologies that do not allow client side scripting.
CAPEC-86 exploits 1 CWE weakness, including CWE-80 (Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)).
MITRE rates CAPEC-86 as Very High severity with high likelihood of attack.
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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