Home > CAPEC List > CAPEC-63: Cross-Site Scripting (XSS) (Version 3.0)  

CAPEC-63: Cross-Site Scripting (XSS)

Attack Pattern ID: 63
Abstraction: Standard
Status: Draft
Presentation Filter:
+ Description
An adversary 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.
+ Likelihood Of Attack

High

+ Typical Severity

Very High

+ Relationships

The table(s) below shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.

+ Relevant to the view "Mechanisms of Attack" (CAPEC-1000)
NatureTypeIDName
ChildOfMeta Attack PatternMeta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.242Code Injection
ParentOfDetailed Attack PatternDetailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.588DOM-Based XSS
ParentOfDetailed Attack PatternDetailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.591Reflected XSS
ParentOfDetailed Attack PatternDetailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.592Stored XSS
CanFollowDetailed Attack PatternDetailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.174Flash Parameter Injection
+ 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. 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. 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.

    Techniques
    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.
    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.
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. Use a list of XSS probe strings to inject script in parameters of known URLs. If possible, the probe strings contain a unique identifier. Use a proxy tool to record results of manual input of XSS probes in known URLs. Use a list of XSS probe strings to inject script into UI entry fields. If possible, the probe strings contain a unique identifier. 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.

    Techniques
    Use a list of XSS probe strings to inject script in parameters of known URLs. If possible, the probe strings contain a unique identifier.
    Use a proxy tool to record results of manual input of XSS probes in known URLs.
    Use a list of XSS probe strings to inject script into UI entry fields. If possible, the probe strings contain a unique identifier.
    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.
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. 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. 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.

    Techniques
    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.
    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.
  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). 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 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).

    Techniques
    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
    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).
  3. Content spoofing: By manipulating the content, the attacker targets the information that the user would like to get from the website. 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.

    Techniques
    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.
+ Prerequisites
Target client software must be a client that allows scripting communication from remote hosts, such as a JavaScript-enabled Web Browser.
+ Skills Required
[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.
[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.
+ Consequences

The table below specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

ScopeImpactLikelihood
Confidentiality
Integrity
Availability
Execute Unauthorized Commands
Integrity
Modify Data
Confidentiality
Read Data
+ 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.
+ Example Instances

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:

<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.

+ Memberships
This MemberOf Relationships table shows additional CAPEC Categories and Views that reference this attack pattern as a member. This information is often useful in understanding where a attack pattern fits within the context of external information sources.
NatureTypeIDName
MemberOfCategoryCategory - A category in CAPEC is a collection of attack patterns based on some common characteristic. More specifically, it is an aggregation of attack patterns based on effect/intent (as opposed to actions or mechanisms, such an aggregation would be a meta attack pattern). An aggregation based on effect/intent is not an actionable attack and as such is not a pattern of attack behavior. Rather, it is a grouping of patterns based on some common criteria.341WASC-08 - Cross-Site Scripting
+ References
[REF-1] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. 2004-02.
+ Content History
Submissions
Submission DateSubmitterOrganization
2014-06-23CAPEC Content TeamThe MITRE Corporation
Modifications
Modification DateModifierOrganization
2017-05-01CAPEC Content TeamThe MITRE Corporation
Updated Activation_Zone, Attack_Prerequisites, Description Summary, Examples-Instances, Payload, Payload_Activation_Impact, Related_Attack_Patterns, Related_Weaknesses, Resources_Required, Typical_Likelihood_of_Exploit
Previous Entry Names
Change DatePrevious Entry Name
2017-05-01Simple Script Injection

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Page Last Updated or Reviewed: July 31, 2018