Adobe Patches XSS Flaw in Flex SDK, Releases Patching Tool

Adobe has closed a vulnerability in the Flex SDK on all operating systems that exposes applications to a cross-site scripting attack.

Adobe has patched a security flaw in its Flex software development kit that could result in a cross-site scripting flaw in the applications built using the SDK.

The bug would have allowed attackers to launch a cross-site scripting attack against applications that had been built using avulnerable version of the Flex SDK, Adobe said in its advisory issued Nov. 30. The vulnerability can be found in the Flex SDK for Windows, Macintosh and Linux operating systems, in versions 3.6 and below as well as 4.5.1 and below, Adobe said. The most recent version is the Flex SDK 4.6.

The Flex SDK is a free and open-source application framework from Adobe that allows developers to easily write applications across a variety of devices and platforms. Flex can be used in conjunction with other tools to build applications for both the Web and mobile platforms such as Apple's iOS, Google's Android and Research in Motion's BlackBerry.

"Adobe recommends users of the Adobe Flex SDK 4.5.1 and earlier 4.x versions, and the Adobe Flex SDK 3.6 and earlier 3.x versions update their software, verify whether any (Shockwave-Flash) SWF files in their applications are vulnerable, and update any vulnerable SWF files using the instructions and tools provided," the company's advisory said.

Adobe rated the vulnerability as important. Flaws with that rating, if exploited, would compromise data security and potentially allow access to confidential data or hijack the computer's processing resources, according to the company's severity rating system.

The technical note accompanying the advisory provides instructions on how to check whether the applications have vulnerable SWF files. It appears from the advisory that the vulnerabilities are in Web-based applications built using the vulnerable SDK versions. Applications based on Adobe AIR appear to be unaffected.

If the application is vulnerable, the developer can download and run the patching tool to either repair the code to close the cross-site scripting flaw or patch Flex and rebuild the application and all libraries to replace vulnerable SWF versions with nonvulnerable ones, Adobe said.

The patching tool requires the Adobe AIR runtime to be installed before it can run and is available only for Windows and Mac OS X systems. Developers on Linux should either find a Windows or Macintosh system to run the tool or skip the patching process altogether and just update Flex and rebuild all affected applications, according to Adobe.

"Most applications will not have any adverse effects from the fix," Adobe wrote in the technical note. However, if the application uses ModuleLoader to load modules from different domains applying the fix, it may cause those modules to no longer load, the company said. It can be fixed by specifying the trustContent or SecurityDomain parameters in the application.

While running the patching tool is sufficient to close the hole in the individual applications, subsequent rebuilds of the application and new applications will still be vulnerable to the cross-site scripting flaw. The patching tool can be used as a quick step, but the SDK should still be updated to prevent the problem from recurring, according to Adobe.

If updating the Flex SDK "will take significant time to complete," the patching tool can be used as a "stopgap solution" and complete the full update afterward, when time allows, Adobe said.