CVE-2021-36967: Windows 10 Privilege Escalation Flaw

CVE-2021-36967 Overview

CVE-2021-36967 is an elevation of privilege vulnerability affecting the Windows WLAN AutoConfig Service (Wlansvc). This service is responsible for managing wireless network connections on Windows systems, and a flaw in its implementation allows attackers with adjacent network access to elevate their privileges without requiring user interaction or prior authentication.

Critical Impact

Successful exploitation allows an attacker on an adjacent network to gain elevated privileges on the target system, potentially achieving full system compromise with high impact to confidentiality, integrity, and availability.

Affected Products

• Microsoft Windows 10 (multiple versions including 1607, 1809, 1909, 2004, 20H2, 21H1)
• Microsoft Windows Server 2016 (including versions 2004 and 20H2)
• Microsoft Windows Server 2019

Discovery Timeline

• 2021-09-15 - CVE-2021-36967 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-36967

Vulnerability Analysis

This elevation of privilege vulnerability exists within the Windows WLAN AutoConfig Service, a critical system component that handles wireless network configuration and connection management. The vulnerability is classified under CWE-269 (Improper Privilege Management), indicating that the service does not properly manage or restrict privileges during certain operations.

The attack requires adjacent network access, meaning the attacker must be on the same network segment as the target. However, once in position, exploitation does not require any privileges or user interaction, making it relatively straightforward for attackers already present on a local network segment.

Root Cause

The root cause of CVE-2021-36967 lies in improper privilege management within the WLAN AutoConfig Service. The service fails to properly validate or restrict privilege levels during specific operations, allowing an attacker to manipulate the service in a way that grants elevated privileges. This type of vulnerability typically occurs when a high-privilege service processes input or requests from lower-privileged contexts without adequate security checks.

Attack Vector

The attack vector for this vulnerability is adjacent network-based. An attacker must have access to the same network segment as the target system, such as being connected to the same wireless network or local area network. From this position, the attacker can exploit the WLAN AutoConfig Service vulnerability without needing any authentication credentials or user interaction on the target system.

The exploitation flow involves sending specially crafted requests or data to the vulnerable WLAN AutoConfig Service, triggering the improper privilege management flaw. Upon successful exploitation, the attacker gains elevated privileges on the target system, potentially achieving SYSTEM-level access.

Detection Methods for CVE-2021-36967

Indicators of Compromise

• Unusual activity or service restarts involving the WLAN AutoConfig Service (Wlansvc)
• Unexpected privilege escalation events on systems with wireless networking enabled
• Anomalous network traffic patterns from adjacent network sources targeting WLAN services
• Event logs showing suspicious interactions with the wlansvc.dll or related components

Detection Strategies

• Monitor Windows Event Logs for suspicious privilege escalation events, particularly those involving network services
• Implement endpoint detection rules to identify abnormal WLAN AutoConfig Service behavior
• Deploy network intrusion detection signatures to identify exploitation attempts from adjacent network segments
• Enable audit logging for Windows services and monitor for unexpected service configuration changes

Monitoring Recommendations

• Configure SentinelOne agents to monitor for privilege escalation patterns associated with Windows services
• Enable verbose logging for the WLAN AutoConfig Service where feasible
• Monitor system integrity for unauthorized modifications to WLAN-related binaries and configurations
• Track lateral movement attempts from devices on adjacent network segments

How to Mitigate CVE-2021-36967

Immediate Actions Required

• Apply the Microsoft security update for CVE-2021-36967 immediately on all affected systems
• Prioritize patching systems with wireless networking enabled that are exposed to untrusted network segments
• Consider temporarily disabling the WLAN AutoConfig Service on systems that do not require wireless connectivity
• Implement network segmentation to limit adjacent network access where possible

Patch Information

Microsoft has released security updates to address this vulnerability as part of their September 2021 security updates. Organizations should apply the appropriate patches for their Windows versions. Detailed patch information and download links are available in the Microsoft Security Advisory for CVE-2021-36967.

Workarounds

• Disable the WLAN AutoConfig Service (Wlansvc) on systems that do not require wireless network functionality using sc config Wlansvc start= disabled
• Implement strict network segmentation to isolate critical systems from untrusted adjacent network segments
• Deploy SentinelOne Singularity platform to detect and block privilege escalation attempts in real-time
• Use network access control (NAC) solutions to restrict which devices can connect to network segments containing sensitive systems

# Disable WLAN AutoConfig Service as a temporary workaround
sc config Wlansvc start= disabled
sc stop Wlansvc

# Verify service is disabled
sc query Wlansvc