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CAPEC-63: Simple Script Injection

 
Simple Script Injection
Definition in a New Window Definition in a New Window
Attack Pattern ID: 63
Abstraction: Standard
Status: Draft
Completeness: Complete
+ Description

Summary

An attacker embeds malicious scripts in content that will be served to web browsers. The goal of the attack is for the target software, the client-side browser, to execute the script with the users' privilege level.

An attack of this type exploits a programs' vulnerabilities that are brought on by allowing remote hosts to execute code and scripts. Web browsers, for example, have some simple security controls in place, but if a remote attacker is allowed to execute scripts (through injecting them in to user-generated content like bulletin boards) then these controls may be bypassed. Further, these attacks are very difficult for an end user to detect.

Attack Execution Flow

Explore
  1. Survey the application for user-controllable inputs:

    Using a browser or an automated tool, an attacker follows all public links and actions on a web site. He records all the links, the forms, the resources accessed and all other potential entry-points for the web application.

    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 in the URL.

    env-Web
    2

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

    env-Web
    3

    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

    Inputs are used by the application or the browser (DOM)

    env-Web
    2Inconclusive

    Using URL rewriting, parameters may be part of the URL path.

    env-Web
    3Inconclusive

    No parameters 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 parameters (POST, GET, COOKIE, etc.) is created by the attacker.
    2Success
    A list of application user interface entry fields is created by the attacker.
    3Success
    A list of resources accessed by the application 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.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Use a list of XSS probe strings to inject script in parameters of known URLs. If possible, the probe strings contain a unique identifier.

    env-Web
    2

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

    env-Web
    3

    Use a list of XSS probe strings to inject script into UI entry fields. If possible, the probe strings contain a unique identifier.

    env-Web
    4

    Use a list of XSS probe strings to inject script into resources accessed by the application. If possible, the probe strings contain a unique identifier.

    env-Web

    Indicators

    IDTypeIndicator DescriptionEnvironments
    1Positive

    The output of pages includes some form of a URL parameter. e.g., ?error="<foobar>'(){};=" becomes "<foobar>'(){}=" in the title of the web page.

    env-Web
    2Positive

    Input content becomes part of the web page.

    env-Web
    3Inconclusive

    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 potential 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 adversaries use.
    2Preventative
    Apply appropriate input validation to filter all user-controllable input of scripting syntax
    3Preventative
    Appropriately encode all browser output to avoid scripting syntax
    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 client software must be a client that allows scripting communication from remote hosts, such as a JavaScript-enabled Web Browser

+ Typical Severity

Very High

+ Typical Likelihood of Exploit

Likelihood: High

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

Description

Classic phishing attacks lure users to click on content that appears trustworthy, such as logos, and links that seem to go to their trusted financial institutions and online auction sites. But instead the attacker appends malicious scripts into the otherwise innocent appearing resources. The HTML source for a standard phishing attack looks like this

(Attack)
 
<a href="www.exampletrustedsite.com?Name=<script>maliciousscript</script>">Trusted Site</a>

When the user clicks the link, the appended script also executes on the local user's machine.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Low

To achieve a redirection and use of less trusted source, an attacker can simply place a script in bulletin board, blog, wiki, or other user-generated content site that are echoed back to other client machines.

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: 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
Integrity
Modify application data
Confidentiality
Read application data
+ Injection Vector

Malicious input delivered through standard content (containing scripts) that is sent to the user's machine, for example HTML page containing JavaScript.

+ Payload

Varies with instantiation of attack pattern. Malicious script payload may be appended to end of legitimate looking link

+ Activation Zone

Client browser, its component libraries, and client network (e.g. Intranet)

+ Payload Activation Impact

Description

Enables attacker to execute scripts to launch attacks on remote client machine and environment. Intranet and local systems may not be patched to the same degree as "externally" facing systems, so simple attacks may identify more victims on an "internal" system such as a corporate Intranet

+ Purposes
  • Penetration
  • Exploitation
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: High
+ Technical Context
Architectural Paradigms
Client-Server
Frameworks
J2EE
.NET
Platforms
All
Languages
JSP
Java
ASP.NET
ASP
PHP
AJAX
+ References
[R.63.1] [REF-2] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
+ Content History
Submissions
SubmitterOrganizationDateSource
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team

Page Last Updated: July 23, 2014