Due to a vulnerability in the Flex SDK, many applications built with Flex are vulnerable to cross-site scripting (XSS) attacks. It's necessary to patch the applications to protect user data.
- All web-based (not AIR-based) applications built using any release of Flex 3.x are vulnerable. (These versions include 3.0, 3.0.1, 3.1, 3.2, 3.3, 3.4, 3.4.1, 3.5, 3.5A, and 3.6.)
- Web-based applications built using any release of Flex 4.x compiled using static linkage of the Flex libraries rather than RSL (runtime shared library) linkage are vulnerable. (Versions affected include 4.0, 4.1, 4.5, and 4.5.1.) However, there are certain cases that involve the use of embedded fonts that aren't vulnerable. AIR-based applications aren't vulnerable.
- Most applications built with Flex 4.x that were compiled in the default way (specifically, using RSL linkage) aren't vulnerable. However, there are rare cases in which they are vulnerable.
- Applications built using any release of Flex before 3.0 are not vulnerable.
- Applications built with Flex that are AIR-based (not web-based) are not vulnerable.
- SWF files that were created without using Flex (such as files created in Adobe Flash Professional) are not vulnerable.
The steps described under Action I, in the Solution section below, include instructions for checking whether your SWF file is vulnerable.
There are two actions you can take to protect your users, which are described here. Adobe recommends that you take Action II, which is sufficient even if you do not take Action 1. However, if you find that Action II takes significant time to complete, you can take Action I as a stopgap solution. Then, complete Action II afterwards, when time allows.
Repair and redeply vulnerable applications. The most reliable way to repair your applications is to follow Action II, described later. However, a faster, simpler way to repair your application SWF file is to install and run the provided SWF-patching tool, APSB11_25_Patch_Tool.air on your application SWF file. This patch produces a patched but otherwise-identical SWF file. You can then swap in the new file to replace the original SWF file on the deployment website.
However, any subsequent rebuilds of your application from source code are still vulnerable unless you also update your SDK to a fixed version. (This prodecure is described in Action II.) Also, the SWF-patching tool works by searching for a known byte sequence in a particular area of the SWF file. SWF files built or post-processed using compilers, optimizers, or obfuscators other than an official Flex compiler from Adobe can be vulnerable. (They can be vulnerable even if the tool reports no vulnerability.) If you have used a custom compiler or post-processor, skip to Action II rather than using the SWF-patching tool.
The SWF-patching tool is only supported on Windows and Mac OS X. Do not use it on Linux systems. If you do not have a Windows or Mac OS X system available, skip to Action II rather than using the SWF-patching tool.
To use the SWF-patching too, do the following:
- Read the license agreement near the bottom of this document, in the section titled Flex Application Patch Tool Update License Agreement,. If you agree to its terms, download and install the SWF-patching tool, APSB11_25_Patch_Tool.air. When downloading, some browsers change the filename extension from .air to .zip. Therefore, make sure that you save or rename it with the .air extension.
- Click Browse and select your SWF file to patch. The SWF file is read, modified, and written to, overwriting the existing SWF file. Be sure that you have backed up the file and have permissions to write to the file. The patch tool writes a log file to the same directory as the selected SWF file. It has the same name as the SWF file, except with .log appended, such as mySWF.swf.log.
- Review the output, which appears in the large white text area. If the tool successfully patches your SWF, the output looks something like the following:
Opening C:\mySWF.swf... Analyzing C:\mySWF.swf... Analyzing potentially vulnerable area... Patch applied in memory. Writing patched SWF to C:\mySWF.swf. Success: C:\mySWF.swf patched!
"SWF is not a Flex application SWF"
|Indicates that key things expected in all application SWF files built with Flex were not found. Verify that the SWF file you selected is an application SWF file built with Flex.|
|"Done analyzing, no vulnerability found"||Indicates that the SWF file is not a Flex SWF file.|
|"No vulnerability found"||Indicates that the SWF file appears to be a Flex SWF file, but does not contain the vulnerability.|
|"SWF is a module SWF, which is not vulnerable"||Indicates that the SWF file appears to be a Flex module, not an application. It's unnecessary to patch modules.|
|"Failed: Vulnerability found, but cannot patch <filename>. Please rebuild SWF using a patched SDK"||
Indicates that the SWF file is configured in a way by which RSLs it loads determines its vulnerability. Therefore, the SWF-patching tool can't patch it (due to the rare situation of being a Flex 4 SWF file using RSLs but containing no locales). Rebuild your application from source after updating to a fixed SDK version, as described in Action II below.
The tool continues to report this same message even after updating to a fixed SDK version. However, your SWF file cannot be attacked as long as it is dependent on RSLs from a fixed SDK version.
|"Failed: Error writing SWF"||Indicates that the SWF file is vulnerable, but could not be patched due to an error writing the changes back to the SWF file on disk. Double-check that you have permissions to write the file.|
|"Vulnerability not found in ABC block for frame 2, SWF may have already been patched"||Usually indicates that the SWF file has already been patched.|
|"Vulnerability not found in ABC block for frame 2"||Indicates that the SWF file appears to be a Flex SWF file but does not contain the vulnerable code.|
If you are familiar with and set up to run Flex command-line tools, you can optionally take the following steps. (For information about setting up and using Flex command-line tools, see opensource.adobe.com/wiki/display/flexsdk/Setup.) By following these steps, you can examine the changes that were made to your SWF file.
function private:ModuleInfo:::load(flash.system:ApplicationDomain, flash.system:SecurityDomain, flash.utils:ByteArray)::void maxStack:3 localCount:6 initScopeDepth:5 maxScopeDepth:6
Adobe recommends that all previously downloaded or installed copies of the Flex SDK that contain the vulnerability are replaced with the patched versions of the SDK.
To minimize the impact to your Flex projects, Adobe has released numerous different fixed versions of the Flex SDK. You can replace each of your vulnerable versions of the SDK with a fixed version that is nearly identical, aside from the fix itself.
To determine which SDK you have, look in the root folder of the SDK. (This folder is commonly inside the “sdks” folder within the Adobe Flash Builder or Adobe Flex Builder folder). View the flex-sdk-description.xml file in a text editor, and look at the “name” tag. Then, see the table below to determine which fixed version of the Flex SDK to use to replace each of your vulnerable versions.
Alternatively, you can upgrade from a lower-numbered version of the SDK to any higher-numbered version of the SDK in the right column above. Or, you can update to the just-released Flex SDK 4.6 (which does not contain the vulnerability). However, in some cases you can encounter additional project migration issues when moving to a higher-versioned SDK.
Furthermore, installing the just-released Flash Builder 4.6 installs Flex SDKs that do not contain the vulnerability (specifically, Flex SDK 3.6A and Flex SDK 4.6). If you have any other SDK versions that were installed separately from Flash Builder 4.6, remove those versions or replace them with fixed versions.
Important: If you changed any files in an existing copy of the SDK, back up your modified files. Then, reapply the changes in the new SDK after replacing the old SDK with the new one. Remember to consider any configuration files you could have changed, such as frameworks\flex-config.xml.
Important: It's necessary for users of Adobe Flash Builder (or Adobe Flex Builder) to take some additional precautions. Before replacing your SDKs, first make sure to back up all your Flash Builder project folders. In addition, note any Flash Builder project customizations, such as changes to how libraries are linked (default or runtime shared library or “merged into code”), or changes to the HTML template. Then, you can verify that they remain applied or reapply them after switching to the fixed SDKs. (It is safest to examine and make note of such customizations before replacing your SDKs, rather than after.) Once you have downloaded the fixed SDK on your local machine, unregister ("uninstall") the vulnerable SDK and register (“install”) your new SDKs in Flash Builder. Exact steps can vary slightly depending on your version of Flash Builder (or Flex Builder). However, in newest versions, you select Preferences in the Window menu (Windows) or under the Flash Builder menu (Mac OS). Then, expand the “Flash Builder” node on the left side of the dialog, and select the “Installed Flex SDKs” node beneath it. Use the Remove and Add buttons to change your registered SDKs. Then, check the checkbox for whichever new SDK you want to use as the default SDK, and click OK. All projects use the new default SDK, assuming you have removed all the old SDKs. To update which SDK an individual project uses (rather than the default), select the root node of the project in the Package Explorer. Then, select Properties in the File menu, select the “Flex (...) Compiler” node on the left side of the dialog. Finally, select Use a specific SDK, select the desired SDK from the pop-up menu, and click OK. Now reapply any necessary project customizations that you noted earlier.
Important: If you have a 3.x SDK with data visualization components (for example, Charts, AdvancedDataGrid, OLAPDataGrid) or automated testing support, copy those files manually from the existing SDK to the corresponding fixed SDK. These files are not part of the standard 3.x SDKs available on the Flex opensource site. Typically, the Flex Builder 3.x or Flash Builder 4.x installer adds these files to your 3.x SDK or the files could have been added manually. Before copying these files, make sure that the destination SDK has the same version number as the original SDK (but with the “A” suffix). If they are the same, then copy the following files, if present, from your existing 3.x SDK to the corresponding fixed SDK:
Data Visualization files:
- optional files:
Once you’ve replaced your vulnerable copies of the Flex SDK with fixed versions, rebuild all your applications with Flex. (To be safe, rebuild Flex libraries as well). Your vulnerable SWF files are then replaced with new, nonvulnerable ones. Finally, if you haven’t already redeployed patched versions of your SWF files as part of Action I above, then redeploy your application. Also redeploy and any accompanying SWF files or SWZ library files.
Most applications don't have any adverse effects from the fix. If your application uses ModuleLoader to load modules from different domains, or uses the ModuleManager to load modules from different domains and doesn't specify a SecurityDomain in the IModuleInfo.load() method, those modules no longer load.
To fix this problem, use a fixed SDK and specify the trustContent parameter on the ModuleLoader. Or, specify the SecurityDomain.currentDomain in the call to IModuleInfo.load().
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