CVE-2021-47889: Softros LAN Messenger Privilege Escalation

CVE-2021-47889 Overview

CVE-2021-47889 is an unquoted service path vulnerability affecting Softros LAN Messenger version 9.6.4. The vulnerability exists in the SoftrosSpellChecker service, where the service executable path contains spaces but is not properly enclosed in quotation marks. This misconfiguration allows local attackers 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 this unquoted service path to achieve privilege escalation by injecting malicious executables that run with SYSTEM-level privileges when the SoftrosSpellChecker service starts.

Affected Products

• Softros LAN Messenger 9.6.4
• SoftrosSpellChecker service component
• Windows installations with Softros Messenger installed in the default C:\Program Files (x86)\ directory

Discovery Timeline

• 2026-01-23 - CVE CVE-2021-47889 published to NVD
• 2026-01-26 - Last updated in NVD database

Technical Details for CVE-2021-47889

Vulnerability Analysis

This vulnerability is classified under CWE-428 (Unquoted Search Path or Element). The SoftrosSpellChecker service is configured with an unquoted executable path pointing to C:\Program Files (x86)\Softros Systems\Softros Messenger\Spell Checker\. Because Windows parses unquoted paths containing spaces by attempting to execute progressively longer path segments, an attacker can exploit this behavior by placing a malicious executable at one of the intermediate path locations.

When the service attempts to start, Windows will first try to execute C:\Program.exe, then C:\Program Files.exe, followed by C:\Program Files (x86)\Softros.exe, and so on. If an attacker has write access to any of these directories and places a malicious executable there, Windows will execute that binary instead of the legitimate service executable.

Root Cause

The root cause of this vulnerability is improper configuration of the Windows service path during the Softros LAN Messenger installation process. The service registration fails to enclose the executable path in double quotation marks, which is required when paths contain space characters. This is a common oversight in software installers that use legacy installation frameworks or manual service registration methods.

Attack Vector

The attack requires local access to the system where Softros LAN Messenger is installed. An attacker with limited user privileges who has write access to one of the path segments (such as C:\ or C:\Program Files (x86)\) can place a malicious executable named appropriately (e.g., Program.exe, Softros.exe, or Softros Systems.exe). When the vulnerable service is restarted—either manually, automatically at system boot, or through social engineering—Windows will execute the attacker's malicious binary with the service account privileges, typically SYSTEM-level access.

The vulnerability exploitation depends on the attacker's ability to write files to specific locations in the file system hierarchy. On properly configured systems, standard users cannot write to C:\ or C:\Program Files (x86)\, which limits the exploitability. However, misconfigured systems with relaxed permissions or scenarios where the attacker already has elevated write permissions make this vulnerability more readily exploitable.

Detection Methods for CVE-2021-47889

Indicators of Compromise

• Presence of unexpected executables named Program.exe, Softros.exe, or Softros Systems.exe in root directories or parent folders of the Softros installation path
• Unusual service behavior or startup failures for the SoftrosSpellChecker service
• Process execution anomalies where unexpected binaries are spawned under the service context
• Modifications to file system permissions in the Softros installation path hierarchy

Detection Strategies

• Deploy endpoint detection rules to monitor for executable creation in C:\, C:\Program Files\, and C:\Program Files (x86)\ directories with names matching path segment patterns
• Implement service configuration auditing to identify services with unquoted paths containing spaces
• Use PowerShell or WMIC queries to enumerate all services with unquoted paths: wmic service get name,pathname | findstr /i /v "\""
• Monitor Windows Security Event Log for service installation or modification events (Event ID 7045)

Monitoring Recommendations

• Configure SentinelOne behavioral AI to detect privilege escalation attempts through service manipulation
• Enable file integrity monitoring on critical system directories to detect unauthorized executable placement
• Set up alerts for new service registrations or modifications to existing service configurations
• Monitor process parent-child relationships for services spawning unexpected child processes

How to Mitigate CVE-2021-47889

Immediate Actions Required

• Audit the SoftrosSpellChecker service configuration to verify the vulnerability exists in your installation
• Manually correct the service path by enclosing it in quotation marks using the Windows Registry or sc config command
• Verify file system permissions ensure standard users cannot write to intermediate path locations
• Consider temporary service disablement if the spell checker functionality is not critical to operations

Patch Information

Review the Softros Official Website for updated versions of Softros LAN Messenger that address this vulnerability. The VulnCheck Advisory on Softros provides additional technical details about the vulnerability. Historical exploit information is available at Exploit-DB #49588.

Workarounds

• Manually fix the unquoted path by modifying the service ImagePath registry value to include proper quotation marks around the full executable path
• Ensure Windows default permissions are enforced, preventing standard users from writing to system directories
• Use application whitelisting solutions to prevent unauthorized executables from running, regardless of their location
• Consider deploying SentinelOne's application control features to restrict which binaries can execute in sensitive directories

# Configuration example
# Fix the unquoted service path using sc command
sc config "SoftrosSpellChecker" binPath= "\"C:\Program Files (x86)\Softros Systems\Softros Messenger\Spell Checker\SpellChecker.exe\""

# Alternatively, modify via Registry (requires administrator privileges)
# Navigate to: HKLM\SYSTEM\CurrentControlSet\Services\SoftrosSpellChecker
# Modify ImagePath value to include quotation marks around the full path