Spider: Using a browser or an automated tool, an attacker records all entry points for inputs that happen to be reflected in a client-side script element. These script elements can be located in the HTML content (head, body, comments), in an HTML tag, XML, CSS, etc.
Use a spidering tool to follow and record all non-static links that are likely to have input parameters (through forms, URL, fragments, etc.) actively used by the Web application.
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.
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.
Manually inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a client-side script elements context and observe system behavior to determine if script was executed.
Manually inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a server-side script elements context and observe system behavior to determine if script was executed.
Use an automated injection attack tool to inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a client-side script elements context and observe system behavior to determine if script was executed.
Use an automated injection attack tool to inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a server-side script elements context and observe system behavior to determine if script was executed.
Use a proxy tool to record results of the created requests.
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.
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).
Content spoofing: By manipulating the content, the attacker targets the information that the user would like to get from the website.
Target software must be able to execute scripts, and also grant the adversary privilege to write/upload scripts.
Typical Likelihood of Exploit
Methods of Attack
The XSS script that is embedded in a given IMG tag can be manipulated to probe a different address on every click of the mouse or other motions that the Ajax application is aware of.
In addition the enumerations allow for the attacker to nest sequential logic in the attacks. While Ajax applications do not open up brand new attack vectors, the existing attack vectors are more than adequate to execute attacks, and now these attacks can be optimized to sequentially execute and enumerate host environments.
Attacker Skills or Knowledge Required
Skill or Knowledge Level: Low
To load malicious script into open, e.g. world writable directory
Skill or Knowledge Level: Medium
Executing remote scripts on host and collecting output
Solutions and Mitigations
Use browser technologies that do not allow client side scripting.
Utilize strict type, character, and encoding enforcement.
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.
Ensure all content that is delivered to client is sanitized against an acceptable content specification.
Perform input validation for all remote content.
Perform output validation for all remote content.
Session tokens for specific host
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.
Privileges are constrained, if a script is loaded, ensure system runs in chroot jail or other limited authority mode
Execute unauthorized code or commands
Run Arbitrary Code
Gain privileges / assume identity
Malicious input delivered through standard script page, e.g. ASP web page
Varies with instantiation of attack pattern. May contain network probe or attacks that run against or on host using host account permissions
Web server scripting host
Payload Activation Impact
Enables attacker to execute scripts on remote host
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Page Last Updated or Reviewed:
July 31, 2017
Use of the Common Attack Pattern Enumeration and Classification dictionary and classification taxonomy, and the associated references from this website, are subject to the