Reviewing Flash Applications

Revision as of 16:15, 15 January 2009 by KirstenS (talk | contribs) (Shared Objects)

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OWASP Code Review Guide Table of Contents

Flash Applications

Look for potential Flash redirect issues.


SandBox Security Model

Flash player assigns SWF files to sandboxes based on their origin.

Internet SWF files sandboxed based on origin domains

Domain: - Any two SWF files can interact together within the same sandbox. - Explicit permission is required to interact with objects in other sandboxes.


local-with-filesystem (default) - The file system can read from local files only

local-with-networking - Interact with other local-with-networking SWF files

local-trusted - Can read from Local files, communicate to any server and access any SWF file.

“The sandbox defines a limited space in which a Adobe Flash movie running within the Adobe Flash Player is allowed to operate. Its primary purpose is to ensure the integrity and security of the client’s machine, and as well as security of any Adobe Flash movies running in the player.”

Cross Domain Permissions: A Flash movie playing on a web browser is not allowed access that is outside the exact domain from which it originated. This is defined in the cross-domain policy file crossdomain.xml. Policy files are used by Flash to permit Flash to load data from servers other than its native domain. If a SWF file wishes to communicate with remote servers it must be granted explicit permission:

    <allow-access-from domain=""/>

The API call loads a cross domain policy from a specified URL which may be different from the crossdomain.xml file.

Accessing JavaScript

A parameter called allowScriptAccess governs if the Flash object has access to external scripts. It can have three possible values: never, same domain, always

 <object id="flash007"> 
   <param name=movie value="bigmovie.swf">
   <embed AllowScriptAccess="always" name='flash007' src="bigmovie.swf"  type="application/x-shockwave-flash"> 

Shared Objects

Shared Objects are designed to store up to 100kb of data relating to a user’s session. They are dependent on host and domain name and SWF movie name.

They are stored in binary format and are not cross-domain by default. Shared objects are not automatically transmitted to the server unless requested by the application.

It is worth noting that they are also stored outside the web browser cache:

C:\Documents and Settings\<USER>\Application Data\Macromedia\Flash Player\#Shared Objects\<randomstring>\<domain>

In the case of cleaning the browser cache Flash sharedobjects survive such an action.

Shared objects are handled by the Flash application and not the clients' web browser.

Permission Structure


  • Any two SWF files can interact within the same sandbox. They need explicit permission to read data from another sandbox


  • local-with-filesystem (default) - can read from local files only
  • local-with-networking
    • Communicate with other local-with-networking SWF files
    • Send data to servers (e.g., using XML.Send() )


  • May read from local files; read or send messages with any server; and script and any other SWF file