CVE-2021-47861: Event Log Explorer Privilege Escalation

CVE-2021-47861 Overview

Event Log Explorer 4.9.3 contains an unquoted service path vulnerability that allows local users to potentially execute arbitrary code with elevated system privileges. Attackers can exploit the unquoted service path by placing malicious executables in specific file system locations that will be executed with LocalSystem account privileges during service startup.

Critical Impact

Local privilege escalation to SYSTEM-level access through unquoted service path exploitation, enabling full compromise of the affected Windows host.

Affected Products

• Event Log Explorer 4.9.3
• ElodeaEventCollectorService component

Discovery Timeline

• 2026-01-21 - CVE CVE-2021-47861 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2021-47861

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 but lack proper quotation marks, the operating system's path resolution mechanism becomes exploitable. The ElodeaEventCollectorService in Event Log Explorer 4.9.3 registers its service binary path without enclosing quotes, creating an opportunity for local attackers to hijack the service execution flow.

The vulnerability requires local access to the system but does not require user interaction for exploitation. Once triggered, the malicious payload executes in the security context of the LocalSystem account, granting the attacker the highest level of privileges on the Windows operating system.

Root Cause

The root cause stems from improper service registration during Event Log Explorer installation. When the ElodeaEventCollectorService is installed, the service binary path is stored in the Windows registry without quotation marks. If this path contains spaces (such as C:\Program Files\Event Log Explorer\service.exe), Windows will attempt to locate executables at truncated path locations before reaching the intended binary.

Attack Vector

The attack requires local access to the target system and write permissions to directories within the unquoted service path. An attacker analyzes the service path structure and identifies potential interception points. For example, if the service path is C:\Program Files\Event Log Explorer\ELEService.exe, Windows will sequentially attempt to execute:

1. C:\Program.exe
2. C:\Program Files\Event.exe
3. C:\Program Files\Event Log\Explorer\ELEService.exe

By placing a malicious executable named Program.exe in the root of C:\ (if write access exists) or similarly named files in other path segments, the attacker can intercept service startup. When the service starts—either through system reboot or manual restart—Windows executes the malicious binary with LocalSystem privileges instead of the legitimate service executable.

Additional technical details regarding exploitation can be found in the Exploit-DB #49704 advisory and the VulnCheck Advisory on Elodea.

Detection Methods for CVE-2021-47861

Indicators of Compromise

• Presence of unexpected executables named Program.exe, Event.exe, or similar in directories along the service path
• Modifications to file permissions in C:\ or C:\Program Files\ directories allowing non-administrative write access
• Unexpected child processes spawned by the ElodeaEventCollectorService
• Registry modifications to the HKLM\SYSTEM\CurrentControlSet\Services\ElodeaEventCollectorService ImagePath value

Detection Strategies

• Query the Windows registry for services with unquoted ImagePath values containing spaces using PowerShell: Get-WmiObject win32_service | Where-Object {$_.PathName -notmatch '^"' -and $_.PathName -match ' '}
• Monitor file creation events in directories that could intercept unquoted service paths (C:\, C:\Program Files\)
• Deploy endpoint detection rules to alert on executables with common interception names (Program.exe, Common.exe) in root or system directories
• Implement SentinelOne Singularity to detect anomalous process execution chains originating from service contexts

Monitoring Recommendations

• Enable Windows Security Event logging for service installation and modification events (Event ID 4697, 7045)
• Configure file integrity monitoring on directories vulnerable to unquoted path exploitation
• Establish baseline of legitimate service executables and alert on deviations during service startup sequences

How to Mitigate CVE-2021-47861

Immediate Actions Required

• Audit the ElodeaEventCollectorService registry entry at HKLM\SYSTEM\CurrentControlSet\Services\ElodeaEventCollectorService and verify the ImagePath value
• Manually correct the service path by adding quotation marks around the executable path in the registry
• Restrict write permissions on directories within the service path to administrative accounts only
• Consider disabling the ElodeaEventCollectorService if not critical to operations until a vendor patch is available

Patch Information

Review the Event Log Explorer vendor website for updated versions that address this vulnerability. Ensure the service path is properly quoted in newer releases before deploying updates.

Workarounds

• Modify the registry value for the ImagePath of ElodeaEventCollectorService to include quotes: change from C:\Program Files\Event Log Explorer\service.exe to "C:\Program Files\Event Log Explorer\service.exe"
• Implement application whitelisting policies to prevent unauthorized executables from running in system directories
• Apply principle of least privilege to restrict which users can write to directories in service execution paths

# Registry fix example (run as Administrator in PowerShell)
# First, backup the current value, then update with quoted path
$serviceName = "ElodeaEventCollectorService"
$regPath = "HKLM:\SYSTEM\CurrentControlSet\Services\$serviceName"
$currentPath = (Get-ItemProperty -Path $regPath -Name ImagePath).ImagePath
# Add quotes if not already present
if ($currentPath -notmatch '^"') {
    Set-ItemProperty -Path $regPath -Name ImagePath -Value "`"$currentPath`""
}