CVE-2021-47825: Acer Updater Privilege Escalation Flaw

CVE-2021-47825 Overview

CVE-2021-47825 is an unquoted service path vulnerability in Acer Updater Service version 1.2.3500.0. This security flaw allows local users to execute arbitrary code with elevated system privileges by exploiting the improperly quoted service path configuration. When the Windows Service Control Manager attempts to start the Acer Updater Service, the unquoted path C:\Program Files\Acer\Acer Updater\ creates an opportunity for attackers to place malicious executables in strategic locations that will be executed with LocalSystem permissions.

Critical Impact

Local attackers with limited privileges can achieve full system compromise by exploiting this unquoted service path to execute malicious code with LocalSystem permissions during service startup.

Affected Products

• Acer Updater Service version 1.2.3500.0
• Windows systems with Acer pre-installed software containing the vulnerable updater service
• Acer devices using the affected UpdaterService.exe component

Discovery Timeline

• 2026-01-16 - CVE CVE-2021-47825 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47825

Vulnerability Analysis

This vulnerability is classified under CWE-428 (Unquoted Search Path or Element), a common Windows privilege escalation technique. The Acer Updater Service is installed with a service binary path that contains spaces but is not enclosed in quotation marks. When Windows attempts to resolve such a path, it sequentially searches for executables at each space-delimited segment of the path.

For the vulnerable path C:\Program Files\Acer\Acer Updater\UpdaterService.exe, Windows will attempt to execute in this order:

1. C:\Program.exe
2. C:\Program Files\Acer\Acer.exe
3. C:\Program Files\Acer\Acer Updater\UpdaterService.exe

An attacker who can write to any of these locations before the legitimate executable is found can achieve code execution with the privileges of the service, which in this case runs as LocalSystem.

Root Cause

The root cause of this vulnerability is improper installation configuration where the service binary path was not properly quoted during service registration. The installer failed to enclose the full path in double quotes when calling the Windows Service Control Manager API. This oversight allows the Windows path resolution mechanism to be exploited when the path contains spaces.

Attack Vector

This is a local attack vector requiring the attacker to have write access to one of the intermediate path locations. The most common exploitation scenario involves placing a malicious executable named Acer.exe in the C:\Program Files\Acer\ directory. When the service starts (either during system boot or when manually triggered), the malicious executable runs with LocalSystem privileges before Windows continues searching for the actual service binary.

The attack requires:

1. Local access to the target system with user-level privileges
2. Write permissions to one of the exploitable path locations
3. The ability to trigger service restart or wait for system reboot

Additional technical details and proof-of-concept information can be found at the Exploit-DB #49890 and the VulnCheck Advisory for Acer.

Detection Methods for CVE-2021-47825

Indicators of Compromise

• Unexpected executables named Program.exe, Acer.exe, or similar in root directories or intermediate paths along the service path
• New or modified files in C:\Program Files\Acer\ that are not part of the legitimate Acer software suite
• Suspicious process creation events showing executables running with SYSTEM privileges from unusual locations
• Windows Event Log entries indicating service startup failures followed by successful starts

Detection Strategies

• Query Windows services for unquoted paths using PowerShell: Get-WmiObject win32_service | Where-Object {$_.PathName -notlike '"*' -and $_.PathName -like '* *'}
• Monitor file creation events in C:\Program Files\Acer\ and parent directories for unexpected executables
• Use SentinelOne Singularity platform to detect anomalous process trees where unexpected executables spawn from service startup contexts
• Implement file integrity monitoring on directories within the vulnerable service path

Monitoring Recommendations

• Enable advanced auditing for file system object access on sensitive directories
• Configure SentinelOne behavioral AI to alert on privilege escalation patterns consistent with unquoted service path exploitation
• Monitor for new service installations or modifications to existing service configurations
• Track process creation events where parent process is services.exe but the child executable is in an unexpected location

How to Mitigate CVE-2021-47825

Immediate Actions Required

• Identify all systems with Acer Updater Service version 1.2.3500.0 installed
• Manually correct the service path by adding quotes around the binary path using the Windows Registry or sc config command
• Audit the vulnerable path locations for any suspicious executables that may have already been placed
• Consider disabling the Acer Updater Service if it is not required for business operations

Patch Information

Users should check the Acer Official Homepage for updated versions of the Acer Updater Service that address this vulnerability. Until an official patch is available, manual remediation of the service path is recommended.

Workarounds

• Manually fix the unquoted path by modifying the registry key at HKLM\SYSTEM\CurrentControlSet\Services\UpdaterService to include quotes around the ImagePath value
• Restrict write permissions on directories along the service path to prevent unauthorized executable placement
• Use application whitelisting solutions to prevent execution of unauthorized executables in vulnerable path locations
• Disable the Acer Updater Service if automatic updates are not required

# Configuration example - Fix unquoted service path
sc config "UpdaterService" binPath= "\"C:\Program Files\Acer\Acer Updater\UpdaterService.exe\""

# Alternative: Using PowerShell to identify and remediate
Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\UpdaterService" -Name ImagePath
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\UpdaterService" -Name ImagePath -Value '"C:\Program Files\Acer\Acer Updater\UpdaterService.exe"'