Friday, November 11, 2005

Technical Description of Sony DRM software

(via F-Secure)

Extended Copy Protection (XCP) is a CD/DVD copy protection technology created by First 4 Internet Ltd. XCP has been used to protect some audio CDs released by Sony BMG Music Entertainment. The XCP protected disks contain digital rights management (DRM) software that allow the user to make a limited number of copies of the disk and also rip the music into a digital format to be used on a computer or portable music player.

Once installed, the DRM software will hide:

Files
Processes
Registry keys and values

No means of uninstalling the DRM software is given. The software supports Windows 98SE, Windows ME, Windows 2000 SP4 and Windows XP.

This analysis was conducted on Windows XP in October 2005. The music CD that contained the DRM software was Van Zant: Get Right with the Man (Sony BMG Music Entertainment).

Installation

The DRM software requires administrative privileges to be installed successfully. When a user inserts an XCP protected CD into a computer that has the Windows Autoplay feature enabled, an EULA is automatically presented and if the user accepts it, the DRM software is installed.

The software installs two services that will start automatically during system startup:

HKLM\SYSTEM\CurrentControlSet\Services\CD_Proxy
HKLM\SYSTEM\CurrentControlSet\Services\$sys$DRMServer

The first on is named 'XCP CD Proxy' and the latter one is named 'Plug and Play Device Manager'. Both services are listed and can be seen by the service control manager.

In addition, it installs five drivers:

HKLM\SYSTEM\CurrentControlSet\Services\$sys$aries
HKLM\SYSTEM\CurrentControlSet\Services\$sys$cor
HKLM\SYSTEM\CurrentControlSet\Services\$sys$crater
HKLM\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_$SYS$OCT
HKLM\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_$SYS$LIM

The first driver hides the presence of the DRM software and the latter drivers act as filter drivers and apparently monitor the CD drives in order to enforce any digital rights.

The files for the software will be installed into the directory 'C:\Windows\System32\$sys$filesystem' that will be hidden but still accessible (a directory listing does not show it, but you can access it if you know the name). Contained in that directory will be the files:

$sys$DRMServer.exe
$sys$parking
aries.sys
crater.sys
DbgHelp.dll
lim.sys
oct.sys
Unicows.dll

Additional installed files are:

C:\windows\CDProxyServ.exe
C:\windows\DbgHelp.dll
C:\windows\system32\$sys$caj.dll
C:\windows\system32\$sys$upgtool.exe
C:\windows\system32\AXPSupport.dll
C:\windows\system32\ECDPlayerControl.ocx
C:\windows\system32\InstallContinue.exe
C:\windows\system32\driver\$sys$cor.sys
C:\windows\system32\TMPX\APIX.vxd
C:\windows\system32\TMPX\ASPIENUM.vxd
C:\windows\system32\TMPX\WNASPI.dll
C:\windows\system32\TMPX\WNASPI32.dll
C:\windows\system32\Unicows.dll

Microsoft C/C++ runtime and XML libraries are also updated, if they have not already been installed by some other application.

It should be noted that if the DRM software is active, the registry keys that start with the string '$sys$' will not be shown by most of the available registry editing tools. Also all files and directories that start with the string '$sys$' will not be visible. In Safe Mode these hiding techniques are not active and all the entries are visible.

Hiding Technique

The DRM software hides it information by modifying the execution path of several Native API functions. Specifically, the aries.sys driver hooks the System Service Table (SST). The following API functions are hooked:

Ntoskrnl.exe:

NtCreateFile
NtEnumerateKey
NtOpenKey
NtQueryDirectoryFile
NtQuerySystemInformation

These hooks are generally used to hide files, folders, registry keys, registry values and processes.

Removing

Uninstallation of the DRM software can currently only be done by sending an uninstallation request to Sony through their customer support. The form can be found here:

http://cp.sonybmg.com/xcp/english/form14.html

Sony has also released an update the disables the hiding features. The updates can be found here:

http://cp.sonybmg.com/xcp/english/updates.html

Conclusion

The DRM software does not self-replicate and doesn't contain malicious features and should thus be considered a false positive, triggered by the advanced hiding techniques used by the software.

Although the software isn't itself malicious, the hiding techniques used are exactly the same that malicious software known as rootkits use to hide themselves. The DRM software will cause many similar false alarms with all AV software that detect rootkits.

The hiding techniques used by the DRM software can be abused by less technical malware authors to hide their backdoors and other tools. If a malware names its files beginning with the prefix '$sys$', the files will also be hidden by the DRM software. Thus it is very inappropriate for commercial software to use these techniques.

Links

First 4 Internet Ltd:

http://www.first4internet.co.uk/

XCP technology:

http://www.xcp-aurora.com/

Sony BMG XCP site:

http://cp.sonybmg.com/xcp/

Technical details: Samuli Larvala, Nov 1st, 2005;
F-Secure Corporation

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