Elevation of Privilege Vulnerability in iTunes for Windows

2010-03-3100:00:00

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Elevation of Privilege Vulnerability in iTunes for Windows

March 31th, 2010

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Summary

Name: Elevation of Privilege Vulnerability in iTunes for Windows
Release Date: March 31th, 2010
Discoverer: Jason Geffner
Vendor: Apple Inc.
Systems Affected: iTunes 9.0.0, iTunes 9.0.1, iTunes 9.0.2, iTunes 9.0.3
(version previous to iTunes 9.0.0 not tested)
Risk: High
Apple Security Advisory ID: APPLE-SA-2010-03-30-2 [1]
Apple Knowledge Base Article: HT4105 [2]
CVE-ID: CVE-2010-0532
Status: Published

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Introduction

This paper discusses how an unprivileged local attacker can elevate their
privileges during an initial installation or update of iTunes for Windows. This
vulnerability was responsibly disclosed to Apple Inc. and this advisory was not
released until a fixed build of iTunes was released.

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Background

"iTunes is a proprietary digital media player application, used for playing and
organizing digital music and video files. The program is also an interface to
manage the contents on Apple's popular iPod and other digital media players
such as the iPhone and iPad. Additionally, iTunes can connect to the iTunes
Store via the Internet to purchase and download music, music videos, television
shows, applications, iPod games, audiobooks, podcasts, feature length films and
movie rentals (not available in all countries), and ringtones (only used for
iPhone). It is also used to download applications for the iPhone and iPod touch
running iPhone OS 2.0 or later." [3]

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Timeline

09/22/09 iTunes 9.0.1 released
10/22/09 Elevation of privilege vulnerability discovered in iTunes 9.0.1
10/22/09 Detailed vulnerability report responsibly disclosed to Apple Inc.
10/22/09 Automated response received from Apple Inc.
10/28/09 Automated response received from Apple Inc.
10/29/09 iTunes 9.0.2 released
12/23/09 Status request sent to Apple Inc.
01/06/10 First personal response formally received from Apple Inc.
02/01/10 iTunes 9.0.3 released
03/30/10 iTunes 9.1.0 released, fixing elevation of privilege vulnerability
03/31/10 Advisory released

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Vulnerability

Upon first-time installation, iTunes installs GEAR Software ASPI driver
components and Microsoft Driver Install Frameworks API components in
"%ALLUSERSPROFILE%\Application Data\{755AC846-7372-4AC8-8550-C52491DAA8BD}\x86"
for 32-bit installations and in "%ALLUSERSPROFILE%\Application Data\
{0DD0EEEE-2A7C-411C-9243-1AE62F445FC3}\x64" for 64-bit installations. The
installer installs in this directory DifXInstall32.exe or DifXInstall64.exe for
32-bit or 64-bit installations, respectively, along with DIFxAPI.dll and other
files. After the installer writes these files to the directory, it will execute
DifXInstall32.exe or DifXInstall64.exe in the context of Local System, a
privileged user.

On a standard Windows installation, unprivileged users have write-access to
"%ALLUSERSPROFILE%\Application Data". As such, prior to a first-time iTunes
installation, an unprivileged attacker can create these directories and place a
malicious executable at "%ALLUSERSPROFILE%\Application Data\
{755AC846-7372-4AC8-8550-C52491DAA8BD}\x86\DifXInstall32.exe" or
"%ALLUSERSPROFILE%\Application Data\{0DD0EEEE-2A7C-411C-9243-1AE62F445FC3}\x64\
DifXInstall64.exe", which could for example add the unprivileged attacker to
the Administrators group in Windows when DifXInstall32.exe or DifXInstall64.exe
is executed by a privileged user. During installation, the installer won't
overwrite an existing DifXInstall32.exe or DifXInstall64.exe; it will execute
the existing program in the context of Local System.

On the other hand, if iTunes is already installed on the system, an
unprivileged attacker won't have access to overwrite DifXInstall32.exe,
DifXInstall64.exe, or DIFxAPI.dll. However, unprivileged attackers still have
write-access to create new files in "%ALLUSERSPROFILE%\Application Data\
{755AC846-7372-4AC8-8550-C52491DAA8BD}\x86" or "%ALLUSERSPROFILE%\
Application Data\{0DD0EEEE-2A7C-411C-9243-1AE62F445FC3}\x64". Therefore, an
unprivileged attacker could place into the directory a malicious DLL that
DifXInstall32.exe, DifXInstall64.exe, or DIFxAPI.dll depends on. For example,
DIFxAPI.dll imports setupapi.dll; an unprivileged attacker could place a
malicious setupapi.dll file into that directory such that when
DifXInstall32.exe or DifXInstall64.exe is executed, it loads DIFxAPI.dll, which
in turn loads the malicious setupapi.dll, which could for example add the
unprivileged attacker to the Administrators group in Windows when
DifXInstall32.exe or DifXInstall64.exe is executed by a privileged user. When
an existing iTunes installation is updated to a newer version, the update
installer will execute DifXInstall32.exe or DifXInstall64.exe in the context of
Local System.

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Exploit

Ideally, the attacker's DLL should have all the functionality of the DLL that
the application expected to load, including the same exported functions. An
attacker can patch the original DLL so that the attacker's code runs before the
DLL's original DllMain code is executed, after which the original DllMain code
is called. This allows the DLL to continue to operate as normal.

The program at http://www.malwareanalysis.com/releases/dllpatcher.zip [4] can be
used to redirect a given DLL's entrypoint (which originally pointed to DllMain)
to point to code that has been patched into the DLL. This patched-in code will
add a given user to the Administrators group in Windows (assuming that it's
being run in the context of a privileged user), after which it will transfer
control back to the DLL's original DllMain. The patcher also updates the Import
Table for the DLL since the patched-in code relies on the function
NetLocalGroupAddMembers(…) from netapi32.dll. The only other side effect of
the patcher is that it clears the Bound Imports for the DLL; the only adverse
side effect of this is that this may cause the DLL to take a few extra
milliseconds to load.

The patcher is compatible with both 32-bit and 64-bit DLLs and displays usage
instructions when executed without command line arguments.

As an example, an attacker could use this patcher as follows to patch
setupapi.dll so that it will add unprivileged user MyComputer\Jason to the
Administrators group when the DLL is loaded by a privileged user:

DllPatcher.exe %WINDIR%\system32\setupapi.dll "%ALLUSERSPROFILE%\Application
Data\{755AC846-7372-4AC8-8550-C52491DAA8BD}\x86\setupapi.dll" MyComputer\Jason

==========
Conclusion

Proper ACLs should be used to prevent such elevation of privilege attacks and
great care should be taken when choosing which directories to use for
executable files.

NGSSoftware would like to thank Alex Ionescu for his assistance in
communications with the Apple Product Security Team.