Hi all,

During installation or update of DisplayLink Core Software 8.2.1956 if it
is executed as SYSTEM, as is the case on many companies,binary cl_1956.exe
(Cleaner Application) is extracted to "%SYSTEMROOT%\Temp" and later
executed as SYSTEM using the command line: "C:\Windows\TEMP\cl_1956.exe"
-min -maxVersion 8.2.1956.0.

This path "%SYSTEMROOT%\Temp" is user writable, at least in win10, and
cl_1956.exe is vulnerable to DLL hijack. It loads several dll which are not
known_dll and you can at least hijack wtsapi32.dll to execute code in the
process context.

An unprivileged local user can copy a self compiled dll with name
wtsapi32.dll to %SYSTEMROOT%\Temp, and gain SYSTEM privileges when
cl_1956.exe loads and executes it.

*Reference*:
https://capec.mitre.org/data/definitions/471.html

*Timeline*
08/03/2018      Vulnerability report sent to the vendor

12/03/2018      Vendor started internal investigation and assigned track
number 27488

04/04/2018       Vendor released first dev version trying to correct the bug

02/05/2018       Vendor released second dev trying to patch the
vulnerability

14/05/2018        Vendor released "Release Candidate" with bug fixed.
.
29/05/2018        Vendor fixed installed can be downloaded from their
website (  http://www.displaylink.com/downloads/windows )

01/06/2018        Report published
-----
Aleix Sala Bach