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CAPEC Details
Name Flash Parameter Injection
Likelyhood of attack Typical severity
High Medium
Summary An adversary takes advantage of improper data validation to inject malicious global parameters into a Flash file embedded within an HTML document. Flash files can leverage user-submitted data to configure the Flash document and access the embedding HTML document. These 'FlashVars' are most often passed to the Flash file via URL arguments or from the Object or Embed tag within the embedding HTML document. If these FlashVars are not properly sanitized, an adversary may be able to embed malicious content (such as scripts) into the HTML document. The injected parameters can also provide the adversary control over other objects within the Flash file as well as full control over the parent document's DOM model. As such, this is a form of HTTP parameter injection, but the abilities granted to the Flash document (such as access to a page's document model, including associated cookies) make this attack more flexible. Flash Parameter Injection attacks can also preface further attacks such as various forms of Cross-Site Scripting (XSS) attacks in addition to Session Hijacking attacks.
Prerequisites
Execution Flow
Step Phase Description Techniques
1 Explore [Spider] Using a browser or an automated tool, an adversary records all instances of HTML documents that have embedded Flash files. If there is an embedded Flash file, they list how to pass global parameters to the Flash file from the embedding object.
  • Use an automated tool to record all instances of URLs which have embedded Flash files and list the parameters passing to the Flash file.
  • Use a browser to manually explore the website to see whether the HTML document has embedded Flash files or not and list the parameters passing to the Flash file.
2 Experiment [Determine the application susceptibility to Flash parameter injection] Determine the application susceptibility to Flash parameter injection. For each URL identified in the Explore phase, the adversary attempts to use various techniques such as DOM based, reflected, flashvars, and persistent attacks depending on the type of parameter passed to the embedded Flash file.
  • When the JavaScript 'document.location' variable is used as part of the parameter, inject '#' and the payload into the parameter in the URL.
  • When the name of the Flash file is exposed as a form or a URL parameter, the attacker injects '?' and the payload after the file name in the URL to override some global value.
  • When the arguments passed in the 'flashvars' attributes, the attacker injects '&' and payload in the URL.
  • If some of the attributes of the <object> tag are received as parameters, the 'flashvars' attribute is injected into the <object> tag without the creator of the Web page ever intending to allow arguments to be passed into the Flash file.
  • If shared objects are used to save data that is entered by the user persistent Flash parameter injection may occur, with malicious code being injected into the Flash file and executed, every time the Flash file is loaded.
3 Exploit [Execute Flash Parameter Injection Attack] Inject parameters into Flash file. Based on the results of the Experiment phase, the adversary crafts the underlying malicious URL containing injected Flash parameters and submits it to the web server. Once the web server receives the request, the embedding HTML document will controllable by the adversary.
  • Craft underlying malicious URL and send it to the web server to take control of the embedding HTML document.
Solutions User input must be sanitized according to context before reflected back to the user. The JavaScript function 'encodeURI' is not always sufficient for sanitizing input intended for global Flash parameters. Extreme caution should be taken when saving user input in Flash cookies. In such cases the Flash file itself will need to be fixed and recompiled, changing the name of the local shared objects (Flash cookies).
Related Weaknesses
CWE ID Description
CWE-88 Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
Related CAPECS
CAPEC ID Description
CAPEC-63 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.
CAPEC-178 An attacker is able to trick the victim into executing a Flash document that passes commands or calls to a Flash player browser plugin, allowing the attacker to exploit native Flash functionality in the client browser. This attack pattern occurs where an attacker can provide a crafted link to a Flash document (SWF file) which, when followed, will cause additional malicious instructions to be executed. The attacker does not need to serve or control the Flash document. The attack takes advantage of the fact that Flash files can reference external URLs. If variables that serve as URLs that the Flash application references can be controlled through parameters, then by creating a link that includes values for those parameters, an attacker can cause arbitrary content to be referenced and possibly executed by the targeted Flash application.
CAPEC-182 An attacker tricks a victim to execute malicious flash content that executes commands or makes flash calls specified by the attacker. One example of this attack is cross-site flashing, an attacker controlled parameter to a reference call loads from content specified by the attacker.
CAPEC-460 An attacker overrides or adds HTTP GET/POST parameters by injecting query string delimiters. Via HPP it may be possible to override existing hardcoded HTTP parameters, modify the application behaviors, access and, potentially exploit, uncontrollable variables, and bypass input validation checkpoints and WAF rules.