Home > CAPEC List > CAPEC-86: Embedding Script (XSS ) in HTTP Headers (Version 2.4)  

CAPEC-86: Embedding Script (XSS ) in HTTP Headers

 
Embedding Script (XSS ) in HTTP Headers
Definition in a New Window Definition in a New Window
Attack Pattern ID: 86
Abstraction: Detailed
Status: Draft
Completeness: Complete
+ Description

Summary

An attack of this type 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.

Attack Execution Flow

Explore
  1. Spider:

    Using a browser or an automated tool, an attacker follows all public links on a web site. He records all the entry points (input) that becomes part of generated HTTP header (not only GET/POST/COOKIE, but also Content-Type, etc.)

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    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.

    env-Web
    2

    Look for HTML meta tags that could be injectable

    env-Web
    3

    Use a proxy tool to record all links visited during a manual traversal of the web application.

    env-Web
    4

    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.

    env-Web

    Indicators

    IDTypeIndicator DescriptionEnvironments
    1Positive

    Web content is generated by the application and served to the browser based on user-controllable inputs.

    env-Web
    2Positive

    HTTP header variables are used by the application or the browser (DOM)

    env-Web
    3Inconclusive

    No HTTP variables appear to be used on the current page. Even though none appear, the web application may still use them if they are provided.

    env-Web
    4Negative

    Applications that have only static pages or that simply present information without accepting input are unlikely to be susceptible.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    A list of URLs, with their corresponding HTTP variables is created by the attacker.

    Security Controls

    IDTypeSecurity Control Description
    1Detective
    Monitor velocity of page fetching in web logs. Humans who view a page and select a link from it will click far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).
    2Detective
    Create links on some pages that are visually hidden from web browsers. Using iframes, images, or other HTML techniques, the links can be hidden from web browsing humans, but visible to spiders and programs. A request for the page, then, becomes a good predictor of an automated tool probing the application.
    3Preventative
    Use CAPTCHA to prevent the use of the application by an automated tool.
    4Preventative
    Actively monitor the application and either deny or redirect requests from origins that appear to be automated.
Experiment
  1. Probe identified potential entry points for XSS vulnerability:

    The attacker 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. He records all the responses from the server that include unmodified versions of his script.

    The attacker 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.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    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.

    env-Web
    2

    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.

    env-Web
    3

    Use a proxy tool to record results of manual input of XSS probes in known URLs.

    env-Web

    Indicators

    IDTypeIndicator DescriptionEnvironments
    1Positive

    User-controllable input is embedded as part of generated HTTP headers

    env-Web
    2Positive

    Input parameters become part of the web page (even in meta tags)

    env-Web
    3Positive

    Output to the browser is not encoded to remove executable scripting syntax.

    env-Web
    4Inconclusive

    Nothing is returned to the web page. It may be a stored XSS. The unique identifier from the probe helps to trace the flow of the possible XSS.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    The attacker's cross-site scripting string is repeated back verbatim at some point in the web site (if not on the same page). Note that sometimes, the payload might be well encoded in the page, but wouldn't be encoded at all in some other section of the same web page (title, script, etc.)
    2Failure
    All HTML-sensitive characters are consistently re-encoded before being sent to the web browser.
    3Inconclusive
    Some sensitive characters are consistently encoded, but others are not.

    Security Controls

    IDTypeSecurity Control Description
    1Detective
    Monitor input to web servers (not only GET, but all in the inputs), application servers, and other HTTP infrastructure (e.g., load balancers). Alert on standard XSS probes. The majority of attackers use well-known strings to check for vulnerabilities. Use the same vulnerability catalogs that hackers use.
    2Preventative
    Apply appropriate input validation to filter all user-controllable input of scripting syntax
    3Preventative
    Do not embed user-controllable input generated HTTP headers
    4Preventative
    Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.
Exploit
  1. Steal session IDs, credentials, page content, etc.:

    As the attacker succeeds in exploiting the vulnerability, he can choose to steal user's credentials in order to reuse or to analyze them later on.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Develop malicious JavaScript that is injected through vectors identified during the Experiment Phase and loaded by the victim's browser and sends document information to the attacker.

    env-Web
    2

    Develop malicious JavaScript that injected through vectors identified during the Experiment Phase and takes commands from an attacker's server and then causes the browser to execute appropriately.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    The attacker gets the user's cookies or other session identifiers.
    2Success
    The attacker gets the content of the page the user is viewing.
    3Success
    The attacker causes the user's browser to visit a page with malicious content.

    Security Controls

    IDTypeSecurity Control Description
    1Detective
    Monitor server logs for scripting parameters.
    2Detective
    Monitor server logs for referrers. If users are being tricked into clicking XSS links through forums or other web postings, their web browsers will be providing Referrer headers most of the time. These can help indicate that the actual request is illegitimate.
    3Preventative
    Apply appropriate input validation to filter all user-controllable input of scripting syntax
    4Preventative
    Appropriately encode all browser output to avoid scripting syntax
    5Preventative
    Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.
  2. Forceful browsing:

    When the attacker targets the current application or another one (through CSRF vulnerabilities), the user will then be the one who perform the attacks without being aware of it. These attacks are mostly targeting application logic flaws, but it can also be used to create a widespread attack against a particular website on the user's current network (Internet or not).

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Develop malicious JavaScript that is injected through vectors identified during the Experiment Phase and loaded by the victim's browser and performs actions on the same web site

    env-Web
    2

    Develop malicious JavaScript that injected through vectors identified during the Experiment Phase and takes commands from an attacker's server and then causes the browser to execute request to other web sites (especially the web applications that have CSRF vulnerabilities).

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    The attacker indirectly controls the user's browser and makes it performing actions exploiting CSRF.
    2Success
    The attacker manipulates the browser through the steps that he designed in his attack. The user, identified on a website, is now performing actions he is not aware of.

    Security Controls

    IDTypeSecurity Control Description
    1Detective
    Monitor server logs for scripting parameters.
    2Detective
    Monitor server logs for referrers. If users are being tricked into clicking XSS links through forums or other web postings, their web browsers will be providing Referrer headers most of the time. These can help indicate that the actual request is illegitimate.
    3Preventative
    Apply appropriate input validation to filter all user-controllable input of scripting syntax
    4Preventative
    Appropriately encode all browser output to avoid scripting syntax
    5Preventative
    Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.
  3. Content spoofing:

    By manipulating the content, the attacker targets the information that the user would like to get from the website.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Develop malicious JavaScript that is injected through vectors identified during the Experiment Phase and loaded by the victim's browser and exposes attacker-modified invalid information to the user on the current web page.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    The user sees a page containing wrong information

    Security Controls

    IDTypeSecurity Control Description
    1Detective
    Monitor server logs for scripting parameters.
    2Detective
    Monitor server logs for referrers. If users are being tricked into clicking XSS links through forums or other web postings, their web browsers will be providing Referrer headers most of the time. These can help indicate that the actual request is illegitimate.
    3Preventative
    Apply appropriate input validation to filter all user-controllable input of scripting syntax
    4Preventative
    Appropriately encode all browser output to avoid scripting syntax
    5Preventative
    Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.
+ Attack Prerequisites
  • Target software must be a client that allows scripting communication from remote hosts, and attacker must control a remote site of some sort to redirect client and data to.

+ Typical Severity

Very High

+ Typical Likelihood of Exploit

Likelihood: High

+ Methods of Attack
  • Injection
  • Modification of Resources
  • Protocol Manipulation
+ Examples-Instances

Description

Utilize a remote style sheet set in the HTTP header for XSS attack. When the attacker 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 attacker. Like most XSS attacks, results vary depending on browser that is used.

(Attack)
 
<META HTTP-EQUIV="Link" Content="<http://ha.ckers.org/xss.css>; REL=stylesheet">

[R.86.2]

Description

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: <META http-equiv="Content-Type" (...) charset=[encoding]/>

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. [R.86.3]

Description

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 attacker can use XSS to mount a DDoS attack by having series of different computers unknowingly executing requests against a single host.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Low

To achieve a redirection and use of less trusted source, an attacker can simply edit HTTP Headers that are sent to client machine.

Skill or Knowledge Level: High

Exploiting a client side vulnerability to inject malicious scripts into the browser's executable process.

+ Resources Required

Ability to deploy a custom hostile service for access by targeted clients. Ability to communicate synchronously or asynchronously with client machine

+ Solutions and 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.

+ Attack Motivation-Consequences
ScopeTechnical ImpactNote
Confidentiality
Integrity
Availability
Execute unauthorized code or commands
Run Arbitrary Code
Confidentiality
Read application data
Confidentiality
Access_Control
Authorization
Gain privileges / assume identity
+ Injection Vector

Malicious input delivered through HTTP Headers.

+ Payload

Varies with instantiation of attack pattern. In the case of HTTP headers they may not be visible to the end user via a browser

+ Activation Zone

Header processing on the server or Client browser

+ Payload Activation Impact

Description

Enables attacker to execute scripts to launch attacks on server as well as remote client machine and environment

+ Purposes
  • Penetration
  • Exploitation
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: High
+ Technical Context
Architectural Paradigms
Client-Server
SOA
Frameworks
All
Platforms
All
Languages
All
+ References
[R.86.1] [REF-2] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
[R.86.2] [REF-9] "OWASP Cheatsheets". XSS Filter Evasion Cheat Sheet. The Open Web Application Security Project (OWASP). <http://ha.ckers.org/xss.html>.
[R.86.3] Watchfire Research. "XSS vulnerabilities in Google.com". Full Disclosure mailing list archives. Dec 21 2005. <http://seclists.org/fulldisclosure/2005/Dec/1107>.
+ Content History
Submissions
SubmitterOrganizationDate
[R.86.1][REF-2] Cigital, Inc2007-01-01
Modifications
ModifierOrganizationDateCommentsSource
Gunnar PetersonCigital, Inc2007-02-28Fleshed out content to CAPEC schema from the original descriptions in "Exploiting Software"
Sean BarnumCigital, Inc2007-03-09Review and revise
Richard StruseVOXEM, Inc2007-03-26Review and feedback leading to changes in Name
Sean BarnumCigital, Inc2007-04-16Modified pattern content according to review and feedback
Romain GaucherCigital, Inc2009-02-10Created draft content for detailed description
Sean BarnumCigital Federal, Inc2009-04-13Reviewed and revised content for detailed description
CAPEC Content TeamThe MITRE Corporation2013-06-21Updated Example-Instance_DescriptionInternal
CAPEC Content TeamThe MITRE Corporation2014-02-06Updated Attack_Phases, Examples-Instances, Solutions_and_MitigationsInternal

Page Last Updated: April 10, 2014