CVE-2016-20091 in Windows Firewall Control
Summary
by MITRE • 06/19/2026
Windows Firewall Control 4.8.6.0 contains an unquoted service path vulnerability that allows local attackers to escalate privileges by inserting malicious executables in the service path. Attackers can place executable files in unquoted path directories that the wfcs.exe service will execute with LocalSystem privileges upon service restart or system reboot.
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Analysis
by VulDB Data Team • 06/23/2026
The Windows Firewall Control 4.8.6.0 application presents a critical privilege escalation vulnerability through an unquoted service path flaw that directly violates security best practices for service configuration management. This vulnerability exists within the wfcs.exe service executable which operates with LocalSystem privileges, creating a dangerous attack surface where malicious actors can inject arbitrary code into the system execution flow. The service path lacks proper quotation marks around directory names containing spaces, allowing Windows to search for executables in parent directories before reaching the intended target location. This design flaw stems from inadequate input validation and secure coding practices that should be enforced according to CWE-428 standards for secure service path handling.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with persistent access to system resources through the Windows Firewall Control service. When the wfcs.exe service restarts or during system reboot cycles, the operating system traverses the unquoted path looking for the executable in a specific order that can be exploited by placing malicious binaries in directories such as C:\Program Files\Windows Firewall Control\ without proper path quoting. This creates a scenario where any user with local access can potentially compromise the entire system through this single vulnerable service, representing a significant risk to enterprise environments where local account access might not be properly restricted.
Security researchers have identified this vulnerability as particularly dangerous because it requires minimal privileges to exploit and offers high-impact results through the execution of malicious code with elevated system privileges. The ATT&CK framework categorizes this type of vulnerability under privilege escalation techniques, specifically targeting service execution and registry modification vectors. The vulnerability demonstrates poor security hygiene in software development practices where services should be configured with proper path quotation using double quotes around directory names containing spaces to prevent command injection attacks. This weakness directly conflicts with Microsoft security recommendations for service configuration and aligns with common attack patterns documented in various threat intelligence reports.
Organizations should immediately implement mitigations including applying vendor patches when available, manually quoting service paths through registry modifications, and implementing strict access controls on system directories where services execute. System administrators must conduct comprehensive audits of all installed services to identify similar vulnerabilities within their environment and ensure proper path quoting for all service executables. The recommended solution involves modifying the service path registry entries to include proper quotation marks around directory names containing spaces, effectively preventing the Windows service manager from traversing unintended directories during executable resolution. Additionally, implementing application whitelisting policies and monitoring for suspicious service execution patterns can provide defense-in-depth protection against exploitation attempts targeting this specific vulnerability class.