CVE-2021-47807: Sync Breeze Privilege Escalation Flaw

CVE-2021-47807 Overview

CVE-2021-47807 is an unquoted service path vulnerability affecting Sync Breeze version 13.6.18 on Windows systems. The vulnerability exists in the Windows service configuration, where the service binary path containing spaces is not properly quoted. This allows local attackers with limited privileges to potentially execute arbitrary code by placing a malicious executable in a location that Windows will execute before the intended service binary.

Critical Impact

Local attackers can exploit unquoted service paths in Sync Breeze to inject malicious executables, potentially achieving privilege escalation to SYSTEM-level access on affected Windows systems.

Affected Products

• Sync Breeze 13.6.18 for Windows
• Windows installations with Sync Breeze services configured in Program Files directories
• Systems where local users have write access to parent directories in the service path

Discovery Timeline

• 2026-01-16 - CVE-2021-47807 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2021-47807

Vulnerability Analysis

This vulnerability falls under CWE-428 (Unquoted Search Path or Element), a configuration flaw that affects how Windows services resolve executable paths. When a Windows service is registered with a path containing spaces and that path is not enclosed in quotes, the Windows Service Control Manager may incorrectly parse the path.

For example, a service path such as C:\Program Files\Sync Breeze Enterprise\bin\syncbrs.exe without quotes can be misinterpreted by Windows. The operating system attempts to execute the following paths in order until it finds a valid executable: C:\Program.exe, C:\Program Files\Sync.exe, and so forth. This behavior creates an opportunity for attackers who can write to these intermediate directories.

The impact of successful exploitation includes complete compromise of the host system, as Windows services typically run under the SYSTEM account. An attacker achieving code execution through this vector inherits those elevated privileges, allowing them to install persistent backdoors, access sensitive data, or pivot to other systems on the network.

Root Cause

The root cause of CVE-2021-47807 is improper quoting of the service binary path in the Windows registry during Sync Breeze installation. The service configuration stored in HKLM\SYSTEM\CurrentControlSet\Services\ contains an ImagePath value without proper quotation marks around paths containing spaces. This is a common oversight in Windows application installers that fail to account for directory names with spaces.

Attack Vector

The attack vector requires local access to the system. An attacker with low privileges must have write access to a directory that appears earlier in the Windows path resolution order, such as C:\Program Files\Sync.exe. Once a malicious executable is placed in one of these locations, the next time the Sync Breeze service starts (either through system reboot, service restart, or crash recovery), Windows will execute the attacker's payload instead of the legitimate service binary.

The attack is particularly dangerous in environments where:

• Multiple users share workstations
• Service accounts have weak permissions
• Automatic service recovery is enabled

Detection Methods for CVE-2021-47807

Indicators of Compromise

• Unexpected executable files in root directories such as C:\Program.exe or C:\Program Files\Sync.exe
• Unusual process execution events where suspicious binaries spawn from service contexts
• Windows Event Log entries showing service startup failures followed by successful starts
• Modified file timestamps in Program Files parent directories

Detection Strategies

• Query Windows services using wmic service get name,pathname | findstr /i /v """ to identify unquoted service paths
• Monitor for file creation events in C:\ and C:\Program Files\ directories that match common truncation patterns
• Use SentinelOne's behavioral AI to detect anomalous service execution patterns
• Implement Sysmon logging with Event ID 11 (FileCreate) for suspicious locations

Monitoring Recommendations

• Enable Windows Security Event logging for service configuration changes (Event ID 7045)
• Deploy file integrity monitoring on directories commonly targeted by unquoted path exploits
• Configure alerts for new executable files created in C:\ or Program Files root directories
• Monitor for services running unexpected binaries through process lineage analysis

How to Mitigate CVE-2021-47807

Immediate Actions Required

• Audit all installed services using PowerShell: Get-WmiObject win32_service | Where-Object {$_.PathName -notlike '"*"' -and $_.PathName -like '* *'}
• Manually quote the affected Sync Breeze service path in the registry
• Restrict write permissions on directories in the service path hierarchy
• Update to a patched version of Sync Breeze if available from the vendor

Patch Information

Refer to the VulnCheck Advisory on SyncBreeze for the latest vendor guidance on patching this vulnerability. Additional technical details are available at Exploit-DB #50023. Organizations should check SyncBreeze Overview for updated versions that address this configuration issue.

Workarounds

• Manually edit the registry to add quotes around the service path at HKLM\SYSTEM\CurrentControlSet\Services\SyncBreeze\ImagePath
• Implement strict file system ACLs to prevent unauthorized users from writing to parent directories
• Consider relocating the application installation to a path without spaces
• Deploy application whitelisting to prevent execution of unauthorized binaries in system directories

# PowerShell command to fix unquoted service path
$serviceName = "SyncBreeze"
$currentPath = (Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\$serviceName" -Name ImagePath).ImagePath
$quotedPath = '"' + $currentPath + '"'
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\$serviceName" -Name ImagePath -Value $quotedPath