CVE-2021-47826: Acer Backup Manager Privilege Escalation

CVE-2021-47826 Overview

CVE-2021-47826 is an unquoted service path vulnerability affecting Acer Backup Manager version 3.0.0.99. The vulnerability exists in the NTI IScheduleSvc service, which uses an unquoted path containing spaces. This configuration flaw allows local users to potentially execute arbitrary code with elevated LocalSystem privileges by placing a malicious executable in a directory that Windows will attempt to execute before reaching the intended service binary.

Critical Impact

Local attackers with limited privileges can achieve privilege escalation to LocalSystem by exploiting the unquoted service path, potentially gaining complete control over affected systems.

Affected Products

• Acer Backup Manager 3.0.0.99
• NTI IScheduleSvc service component
• Systems with Acer Backup Manager installed in C:\Program Files (x86)\NTI\Acer Backup Manager\

Discovery Timeline

• 2026-01-16 - CVE-2021-47826 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47826

Vulnerability Analysis

This vulnerability stems from improper handling of the Windows service executable path for the NTI IScheduleSvc service. When Windows services are configured with paths that contain spaces but are not enclosed in quotation marks, the Windows Service Control Manager (SCM) attempts to locate the executable using a predictable search order. For a path like C:\Program Files (x86)\NTI\Acer Backup Manager\IScheduleSvc.exe, Windows will sequentially attempt to execute:

1. C:\Program.exe
2. C:\Program Files.exe
3. C:\Program Files (x86)\NTI\Acer.exe
4. C:\Program Files (x86)\NTI\Acer Backup.exe

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

Root Cause

The root cause is classified as CWE-428 (Unquoted Search Path or Element). The service registration in the Windows registry stores the executable path without enclosing quotation marks. This is a common configuration oversight during software installation that creates an exploitable privilege escalation vector when combined with weak filesystem permissions.

Attack Vector

Exploitation requires local access to the target system. The attacker must have write permissions to one of the directories in the search path hierarchy. While C:\Program Files and C:\Program Files (x86) are typically protected, custom ACLs, misconfigured permissions, or writable parent directories can provide the necessary access. Once a malicious executable is placed in position, the service must be restarted (or the system rebooted) for the payload to execute with LocalSystem privileges.

The attack flow involves:

1. Identifying the vulnerable unquoted service path
2. Locating a writable directory in the path search order
3. Placing a malicious executable with an appropriate name
4. Waiting for or triggering a service restart to execute the payload

Detection Methods for CVE-2021-47826

Indicators of Compromise

• Unexpected executable files named Program.exe, Files.exe, Acer.exe, or Backup.exe in C:\, C:\Program Files (x86)\, or C:\Program Files (x86)\NTI\ directories
• Unusual process execution originating from the NTI IScheduleSvc service
• New or modified executables in the Acer Backup Manager installation path
• Anomalous LocalSystem process activity following service restarts

Detection Strategies

• Monitor Windows registry for unquoted service paths using queries against HKLM\SYSTEM\CurrentControlSet\Services
• Implement file integrity monitoring on directories in the service path hierarchy
• Deploy endpoint detection rules for executable creation in common exploitation paths
• Use SentinelOne's behavioral AI to detect privilege escalation attempts through service manipulation

Monitoring Recommendations

• Enable Windows Security Event logging for service configuration changes (Event ID 7045)
• Monitor process creation events for unexpected executables running as LocalSystem
• Implement real-time alerting on file writes to C:\Program Files (x86)\NTI\ with suspicious naming patterns
• Regularly audit service configurations for unquoted paths across the environment

How to Mitigate CVE-2021-47826

Immediate Actions Required

• Audit all Acer Backup Manager installations for the vulnerable version 3.0.0.99
• Verify and correct the service path by adding quotation marks around the executable path in the registry
• Review filesystem permissions on directories in the service path to ensure only administrators have write access
• Consider disabling or removing Acer Backup Manager if not actively needed

Patch Information

No vendor patch information is currently available in the NVD database. Organizations should monitor the Acer Official Website for security updates. Additional technical details are available in the VulnCheck Advisory on Acer Backup Manager and Exploit-DB #49889.

Workarounds

• Manually quote the service path by modifying the registry key at HKLM\SYSTEM\CurrentControlSet\Services\NTI IScheduleSvc to include quotation marks around the ImagePath value
• Restrict write permissions on all directories in the service path hierarchy to administrators only
• Implement application whitelisting to prevent unauthorized executables from running
• Use SentinelOne endpoint protection to detect and block exploitation attempts in real-time

# Registry fix to quote the service path
reg add "HKLM\SYSTEM\CurrentControlSet\Services\NTI IScheduleSvc" /v ImagePath /t REG_EXPAND_SZ /d "\"C:\Program Files (x86)\NTI\Acer Backup Manager\IScheduleSvc.exe\"" /f