Advisory ID: SYSS-2021-058  
Product: Razer Synapse  
Manufacturer: Razer Inc.  
Affected Version(s): Versions prior to 3.7.0228.022817  
Tested Version(s): 3.6.0920.091710, 3.6.1010.101113,   
3.6.1130.111217, 3.6.1201.111814,   
Vulnerability Type: Improper Privilege Management (CWE-269)  
Risk Level: Critical  
Solution Status: Fixed  
Manufacturer Notification: 2021-10-18  
Solution Date: 2022-03-07  
Public Disclosure: 2022-03-23  
CVE Reference: CVE-2021-44226  
Authors of Advisory: Dr. Oliver Schwarz, SySS GmbH  
Matthias Deeg, SySS GmbH  
Razer Synapse is an additional driver software for Razer gaming devices.  
The manufacturer describes the product as a "unified cloud-based hardware  
configuration tool" (see [1]).  
Due to an unsafe installation path and improper privilege management,  
the associated system service "Razer Synapse Service" is vulnerable to  
DLL hijacking.  
As a result, local Windows users can abuse the Razer driver installer to  
obtain administrative privileges on Windows.  
In order to exploit the vulnerability, the attacker needs physical  
access to the machine and needs to prepare the attack before Razer  
Synapse is installed along with a Razer driver.  
Vulnerability Details:  
The attack scenario considers a Windows machine without any previous  
installation of any Razer device or software.  
The attacker has a local unprivileged Windows account, physical access  
to the machine, and a device which is either a Razer peripheral or able  
to pretend to be one (such as a Bash Bunny or a Raspberry Pi Zero).  
The attacker aims at executing code with full system privileges.  
The attack exploits the Razer Synapse Service which runs with elevated  
privileges. While the main binary of the service is stored in the  
protected location "C:\Program Files (x86)\Razer\Synapse3\Service", it  
dynamically loads libraries from  
Before the installation, standard users can write to this path, since  
"C:\ProgramData" is world-writable on a standard installation of Windows.  
The Synapse installation procedure changes access privileges, so that  
standard users cannot write to the path any longer. In addition, it  
removes any previous files in that location.  
Furthermore, upon service start, the location is checked for DLLs that  
do not originate from Razer.  
However, if the path is created before the driver installation, the  
creator remains owner of the object and can still change directory and  
file permissions. In particular, the creator can deny access for the  
SYSTEM user and grant access for the attacker's user.  
The attack consists of three phases:  
1. Before the installation of the driver/Synapse, the attacker creates  
"C:\ProgramData\Razer\Synapse3\Service" and denies write-access for  
2. Afterwards, the attacker triggers the installation of Synapse.  
This can be done without any elevated privileges by plugging in a  
Razer device and following the installation procedure for Synapse,  
if device-specific co-installers are not disabled.  
Alternatively, a device such as Bash Bunny or a Raspberry Pi Zero  
can be used and pretend to be a Razer device.  
3. After the installation of Synapse has finished, the attacker grants  
full access to "C:\ProgramData\Razer\Synapse3" for both the SYSTEM  
user and the own low-privileged user account. Afterwards, the  
attacker places a prepared set of DLLs into  
"C:\ProgramData\Razer\Synapse3\Service\bin" and restarts the Razer  
Synapse Service, typically, by restarting the machine.  
SySS GmbH chose the following set of DLLs for a proof of concept:  
* RzLightingEngine.dll from the original installation  
* RSy3_LightingEffects.dll from the original installation  
* userenv_orig.dll, a copy from the standard Windows DLL at  
* userenv.dll, a malicious 32-bit DLL that creates a new admin user  
and redirects to userenv_orig.dll otherwise  
The attack has been successfully tested for the following versions of  
Razer Synapse:  
* 3.6.0920.091710  
* 3.6.1010.101113  
* 3.6.1018.101823  
* 3.6.1130.111217  
* 3.6.1201.111814  
A modified version of the exploit has been successfully tested  
against version 3.7.0131.011810.  
The attack has been successfully tested on the following versions of  
* Windows 10 Enterprise 20H2 19042.1237  
* Windows 10 Pro 20H2 19042.1237  
* Windows 10 Pro 21H1 19043.1237  
* Windows 10 Pro 21H1 19043.1266  
Razer has published a patched version that will be deployed automatically  
upon driver installation on current Windows builds.  
To prevent similar attacks through other co-installers, system  
administrators can disable them by setting the following key in the  
Windows registry:  
Installer\DisableCoInstallers = 1  
Disclosure Timeline:  
2021-10-07: Vulnerability discovered  
2021-10-11: Initial contact to Razer support  
2021-10-18: Vulnerability reported to manufacturer  
2022-01-18: First direct contact with developer team  
2022-02-03: First fix attempt (3.7.0131.011810) announced to SySS GmbH  
2022-03-07: Final fix (3.7.0228.022817) announced to SySS GmbH  
2022-03-23: Public disclosure of vulnerability  
[1] Product website for Razer Synapse 3  
[2] SySS Security Advisory SYSS-2021-058  
[3] SySS Responsible Disclosure Policy  
[4] SySS Proof of Concept Video  
This security vulnerability was found by Dr. Oliver Schwarz of SySS GmbH.  
Public Key:  
Key ID: 0x9716294F1294280D  
Key Fingerprint: D452 B014 E992 2886 E799 6B43 9716 294F 1294 280D  
The information provided in this security advisory is provided "as is"  
and without warranty of any kind. Details of this security advisory may  
be updated in order to provide as accurate information as possible. The  
latest version of this security advisory is available on the SySS website.  
Creative Commons - Attribution (by) - Version 3.0