CAPEC-174 - Flash Parameter Injection

An attacker injects values to global parameters into a Flash movie embedded in an HTML document. These injected parameters are controlled through arguments in the URL used to access the embedding HTML document. 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. The injected parameters can allow the attacker to control other objects within the Flash movie as well as full control over the parent document's DOM model.

Severity

Likelihood

Confidentiality

Integrity

Availability

  • Attack Methods 1
  • Injection
  • Purposes 2
  • Penetration
  • Exploitation
  • Scopes 2
  • "Varies by context"
  • Confidentiality
  • Execute unauthorized code or commands
  • Authorization

Medium level: The attacker need inject values into the global parameters to the Flash movie and understand the parent HTML document DOM structure. The attacker need be smart enough to convince the victim to his crafted link.

The attacker must convince the victim to click their crafted link.

Step 1 - Spider

Using a browser or an automated tool, an attacker records all instances of HTML documents that have embedded Flash movies. If there is an embedded Flash movie, he lists how to pass global parameters to the Flash movie from the embedding object..

Tecnique ID: 1 - Environment(s) env-Web

Use an automated tool to record all instances of URLs which have embedded Flash movies and list the parameters passing to the Flash movie.

Tecnique ID: 2 - Environment(s) env-Web

Use a browser to manually explore the website to see whether the HTML document has embedded Flash movies or not and list the parameters passing to the Flash movie.

Indicator ID: 1 - Environment(s) env-Web

Type: Positive

The HTML document has embedded Flash movies.

Indicator ID: 2 - Environment(s) env-Web

Type: Inconclusive

The HTML file doesn't appear to contain Flash movies, but Ajax request seems possible and could insert Flash movies.


Security Control ID: 1

Type: Detective

Monitor velocity of page fetching in web logs. Humans who view a page and select a link from it will click far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).


Outcome ID: 1

Type: Success

A list of URLs which has embedded Flash movies and the list of parameters passing to the Flash movies.



Step 1 - 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 attack attempts to use various techniques such as DOM based, reflected, flashvars, persistent attacks depending on the type of parameter passed to the embedded Flash movie..

Tecnique ID: 1 - Environment(s) env-Web

When the JavaScript 'document.location' variable is used as part of parameter, inject '#' and payload into the parameter in the URL.

Tecnique ID: 2 - Environment(s) env-Web

When the name of the Flash movie is exposed as a form or a URL parameter, the attacker injects '?' and payload after the movie name in the URL to overrides some global value.

Tecnique ID: 3 - Environment(s) env-Web

When the arguments passed in the 'flashvars' attributes, the attacker injects '&' and payload in the URL.

Tecnique ID: 4 - Environment(s) env-Web

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.

Tecnique ID: 5 - Environment(s) env-Web

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 movie is loaded.

Security Control ID: 1

Type: Preventative

User input must be sanitized according to context before reflected back to the user.


Outcome ID: 1

Type: Success

At least one URL is found susceptible to flash parameter injection.

Outcome ID: 2

Type: Failure

No URL is found susceptible to injection.



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).