Cimetrics BACstac Routing Service 6.2f Local Privilege Escalation

Title: Cimetrics BACstac Routing Service 6.2f Local Privilege Escalation
Advisory ID: ZSL-2017-5397
Type: Local
Impact: Privilege Escalation
Risk: (3/5)
Release Date: 12.02.2017
BACstac belongs to product BACstac(TM) Networking Software and was developed by company Cimetrics Inc. Cimetrics is excited to announce a new version of our industry-leading BACnet protocol stack: BACstac 6.8. The Cimetrics BACstac saves man-years of development when your company needs to create a BACnet solution ! Our software team has created a set of BACnet libraries which greatly simplify the task of interfacing to BACnet.

Even the largest companies in the HVAC industry use our code because it is a very complex and time consuming task keeping up with the ongoing changes that are taking place in the BACnet committees. For example, many hundreds of protocol modifications, requirements, and enhancements have taken place in just the past year. By purchasing the Cimetrics BACstac solution, we do the compatibility coding and testing. This typically saves man-years of software developer time EVERY YEAR !
The application suffers from an unquoted search path issue impacting the service 'bacstac' (bacstac-gtw.exe) for Windows deployed as part of BACstac routing service solution. This could potentially allow an authorized but non-privileged local user to execute arbitrary code with elevated privileges on the system. A successful attempt would require the local user to be able to insert their code in the system root path undetected by the OS or other security applications where it could potentially be executed during application startup or reboot. If successful, the local user’s code would execute with the elevated privileges of the application.

BACstac also provides a named pipe used for IPC connection between a BACstac application and the BACstac service.

The BACstac Service implements AL multiplexing using a custom IPC mechanism. The IPC mechanism was chosen to allow portability to embedded systems, and it uses a fixed number of slots. The slots are recycled when an application stops running.

With Object-based multiplexing, Service requests that identify a particular Object (e.g. Read-Property) can be forwarded to a dedicated process. A multiplexing server using an appropriate IPC mechanism (e.g. CORBA, COM, or UDP) can be built on top of the BACstac API.

A number of BACstac protocol stack run-time configuration parameters are stored in the Windows Registry. These values are created and initialized when the protocol stack is installed. The registry entries are not completely removed when the protocol stack is uninstalled (this is standard behaviour for .INF files). The Registry entries are located in:


The BACstac Service parameters (in ..\Services\BACstac) include plenty of keys, one of which is the 'Tsml\ConnIpc' key with the default name: \\.\pipe\bacstac.

The vulnerability exist due to the improper permissions, with the 'F' flag (Full) for 'Everyone' group.
Cimetrics, Inc. -
Affected Version
Tested On
Microsoft Windows 7 Professional SP1 (EN)
Microsoft Windows 7 Ultimate SP1 (EN)
Vendor Status
[13.12.2016] Vulnerability discovered.
[31.01.2017] Vendor contacted.
[11.02.2017] No reply from the vendor.
[12.02.2017] Public security advisory released.
Vulnerability discovered by Gjoko Krstic - <>
[12.02.2017] - Initial release
[18.02.2017] - Added reference [1], [2], [3] and [4]
Zero Science Lab