Reviewing Flash Applications

OWASP Code Review Guide Table of Contents

Flash Applications
Look for potential Flash redirect issues

clickTAG TextField TextArea load getURL NetConnection.connect NetServices.createGatewayConnection NetSteam.play XML.send

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

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 Macromedia Flash movie running within the Macromedia 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 Macromedia Flash movies running in the player.”

Cross Domain Permissions: A Macromedia Flash movie playing on a web browser is not allowed access that is outside the exact domain from which is 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:

  

The API call System.security.loadPolicyFile(url) 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

 

Permission Structure Shared Objects External Resources, Controlling access Top Tips