CVE-2021-47898: Epson USB Display Privilege Escalation

CVE-2021-47898 Overview

CVE-2021-47898 is an unquoted service path vulnerability affecting Epson USB Display version 1.6.0.0. The vulnerability exists in the EMP_UDSA service, which runs with LocalSystem privileges. Due to improper quoting of the service executable path, attackers with local access can exploit the unquoted path by placing malicious executables in intermediate directories to gain elevated system access.

Critical Impact

Local attackers can achieve privilege escalation to SYSTEM-level access by exploiting the unquoted service path, potentially leading to complete system compromise.

Affected Products

• Epson USB Display version 1.6.0.0
• Systems running the EMP_UDSA service with LocalSystem privileges

Discovery Timeline

• 2026-01-23 - CVE-2021-47898 published to NVD
• 2026-01-26 - Last updated in NVD database

Technical Details for CVE-2021-47898

Vulnerability Analysis

This vulnerability is classified under CWE-428 (Unquoted Search Path or Element). When Windows services are configured with executable paths that contain spaces and are not properly quoted, the operating system's path resolution mechanism can be exploited. The EMP_UDSA service runs with the highest possible privileges (LocalSystem), making it an attractive target for privilege escalation attacks.

The attack requires local access to the system, meaning an attacker must already have a foothold on the target machine. However, once exploited, the attacker can escalate from a low-privileged user account to full SYSTEM-level access, bypassing normal security boundaries.

Root Cause

The root cause of this vulnerability is the improper configuration of the Windows service path for the EMP_UDSA service. When the service executable path contains spaces and is not enclosed in quotation marks, Windows attempts to parse the path by splitting on spaces, trying each possible interpretation as a potential executable location.

For example, if the service path is C:\Program Files\Epson\USB Display\service.exe, Windows will attempt to execute in order:

1. C:\Program.exe
2. C:\Program Files\Epson\USB.exe
3. C:\Program Files\Epson\USB Display\service.exe

Attack Vector

The attack vector is local, requiring an attacker to have initial access to the target system. The exploitation process involves:

1. Identifying the unquoted service path through enumeration of Windows services
2. Placing a malicious executable (such as Program.exe or another appropriately named file) in a location that Windows will attempt to execute before reaching the legitimate service executable
3. Triggering or waiting for the service to restart, at which point Windows executes the malicious payload with LocalSystem privileges

The attacker must have write access to one of the intermediate directories in the path. This is often possible in misconfigured environments or through chained exploitation with other vulnerabilities.

Detection Methods for CVE-2021-47898

Indicators of Compromise

• Unexpected executables named Program.exe, USB.exe, or similar in root directories or intermediate paths
• Suspicious process creation events from service host processes
• New files appearing in C:\ or C:\Program Files\Epson\ directories that match exploitable path segments
• Anomalous LocalSystem process activity originating from non-standard executable paths

Detection Strategies

• Query Windows services for unquoted paths using PowerShell or WMI: Get-WmiObject win32_service | Where-Object {$_.PathName -like '* *' -and $_.PathName -notlike '"*'}
• Monitor file system changes in root directories and common installation paths for new executable files
• Implement endpoint detection rules for service path exploitation techniques
• Use SentinelOne's behavioral AI to detect anomalous privilege escalation patterns

Monitoring Recommendations

• Enable Windows Security Event logging for service configuration changes (Event ID 7045)
• Monitor process creation events for executables running from unusual paths with SYSTEM privileges
• Implement file integrity monitoring on directories commonly targeted by unquoted path attacks
• Configure alerts for any new executables created in C:\ or intermediate Program Files directories

How to Mitigate CVE-2021-47898

Immediate Actions Required

• Audit all Windows services for unquoted paths using native tools or security scanning software
• Restrict write permissions on root directories and intermediate paths to administrators only
• Contact Epson for updated software versions that address the service path configuration
• Consider temporarily disabling the EMP_UDSA service if USB display functionality is not critical

Patch Information

No specific patch information is available from the vendor at this time. Organizations should monitor the Epson Official Website for security updates and updated driver packages that address this vulnerability. Additional technical details are available in the VulnCheck Advisory on Epson Vulnerability and the Exploit-DB #49548 entry.

Workarounds

• Manually correct the service path by adding quotation marks around the executable path in the Windows Registry
• Implement application control policies to prevent execution of unauthorized binaries in intermediate directories
• Deploy SentinelOne endpoint protection to detect and block privilege escalation attempts
• Restrict local user permissions to prevent writing executables to exploitable directories

# Manual remediation: Correct the unquoted service path in Windows Registry
# Run in elevated PowerShell

# Query current service path
$servicePath = (Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\EMP_UDSA").ImagePath

# Add quotes if path contains spaces and is unquoted
if ($servicePath -match ' ' -and $servicePath -notmatch '^"') {
    Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\EMP_UDSA" -Name "ImagePath" -Value "`"$servicePath`""
    Write-Host "Service path has been quoted. Restart the service for changes to take effect."
}