Headbang: Chrome, Flash and AppLocker Don’t Play Together

Google Chrome has bundled  a private copy of Flash since 5.0.375.86. Flash is packaged as gcswf32.dll in the Chrome application folder. All of the EXE and DLL files that come with Chrome as cryptographically signed by Google except for gcswf32.dll which is not signed at all. However, the NSAPI compatible Flash plugin distributed by Adobe is signed by Adobe.

This matters if you are using AppLocker DLL rules to define execution rules because there is no good way to create a permit rule for this DLL. AppLocker is a component of Windows 7 Enterprise and Ultimate SKUs which provides a straightforward mechanism for configuring Windows with a usable default-deny execution policy.

If you enable AppLocker EXE and DLL rules with the default rule set, Chrome will not run at all because Chrome is installed into the %userprofile%\AppData\AppData\Google\Chrome directory structure which is writable by unprivileged users. The obvious solution is to create EXE and DLL rules to permit code published by Google to execute. This works great, except that Flash will not execute. Why oh why is gcswf32.dll not signed by either Google or Adobe? There’s no way to whitelist this DLL except creating a permit *\gcswf32.dll rule or giving up on DLL rules altogether.

Workaround

A viable workaround is to use about:plugins to disable the Flash plugin Google distributes and globally install the “Flash player for Firefox, Mozilla, Netscape, Opera (and other plugin-based browsers)”. This plugin gets installed into C:\Windows\SysWOW64\Macromed\Flash on x64 or C:\Windows\system32\Macromed\Flash on x86 (and is signed by Adobe) is whitelisted by the default DLL rule set because it is inside of the Windows directory.

applocker-exeapplocker-dlldisable-chrome-bundled-flash

Chrome Team, Please Fix Me

You have to disable the bundled Flash player bundled by Chrome in order for Flash to work under this scenario, which means this is a workaround that is not enterprise ready unless your company is full of nerds. Also, this means that I have to worry about updating Flash instead of Chrome just handling it.

AppLocker is good stuff. Chrome is good stuff. I’d these technologies to play better together.

All Google needs to do is distribute a signed version of the Flash player plugin. Why aren’t they already doing this, anyway?

Please Chrome team, this is trivial to fix. Thanks in advance.

Reported as issue 65322.

Edit

A reasonable solution is to use the Chrome enterprise MSI installer which installs Chrome into the standard “program files'” location which means the default AppLocker permit rule on “program files” covers Chrome.

Update

I’m not sure when Google started distributing signed versions of Flash but in Chrome 12, gcswf32.dll comes with a valid signature from Adobe.

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