CVE-2022-44670: Windows SSTP RCE Vulnerability

CVE-2022-44670 Overview

CVE-2022-44670 is a Remote Code Execution (RCE) vulnerability affecting the Windows Secure Socket Tunneling Protocol (SSTP) component across a wide range of Microsoft Windows operating systems. This vulnerability allows an unauthenticated attacker to execute arbitrary code on affected systems by exploiting a Time-of-Check Time-of-Use (TOCTOU) race condition in the SSTP protocol implementation. Due to the network-based attack vector and the potential for complete system compromise, this vulnerability represents a significant threat to enterprise environments relying on SSTP for secure VPN connectivity.

Critical Impact

Successful exploitation could allow remote attackers to execute arbitrary code with SYSTEM privileges on Windows servers configured with SSTP VPN services, potentially leading to complete network compromise.

Affected Products

• Microsoft Windows 10 (multiple versions including 1607, 1809, 20H2, 21H1, 21H2, 22H2)
• Microsoft Windows 11 (including 22H2)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022

Discovery Timeline

• 2022-12-13 - CVE-2022-44670 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-44670

Vulnerability Analysis

This vulnerability stems from a race condition (CWE-367: Time-of-Check Time-of-Use) within the Windows SSTP implementation. SSTP is a VPN protocol that encapsulates PPP traffic over an SSL/TLS channel, commonly used for secure remote access in enterprise environments. The vulnerability exists because the SSTP service improperly handles the timing between checking a resource state and using that resource, creating a window of opportunity for exploitation.

The attack requires no authentication and can be initiated remotely over the network. However, exploitation complexity is considered high because the attacker must win a race condition—precise timing is required to manipulate the resource state between the check and use operations. If successful, the attacker gains the ability to execute arbitrary code with the same privileges as the SSTP service, which typically runs with SYSTEM-level privileges on Windows servers.

The vulnerability affects both client and server Windows installations, though the primary concern is for systems running SSTP-based VPN services. Organizations utilizing Remote Access Server (RRAS) with SSTP are particularly at risk.

Root Cause

The root cause is a Time-of-Check Time-of-Use (TOCTOU) race condition vulnerability classified under CWE-367. In this type of flaw, the software checks the state of a resource at one point in time and uses that resource at a later point, assuming the state has not changed. An attacker who can modify the resource between the check and use operations can cause the software to perform unintended actions, potentially leading to code execution. In the context of SSTP, this race condition exists in how the protocol implementation handles certain protocol operations or memory objects.

Attack Vector

The attack vector is network-based, meaning an attacker can exploit this vulnerability remotely without requiring local access to the target system. The attack scenario involves:

1. The attacker establishes or initiates an SSTP connection to a vulnerable Windows system running SSTP services
2. During the protocol handshake or subsequent communication, the attacker sends specially crafted packets designed to trigger the race condition
3. By precisely timing the malicious input, the attacker exploits the window between when the SSTP service checks a resource and when it uses that resource
4. Successful exploitation allows the attacker to corrupt memory or redirect execution flow, ultimately achieving remote code execution

The exploitation requires winning a race condition, which introduces complexity and may require multiple attempts. However, this should not diminish the severity since automated exploitation tools can rapidly retry until successful.

Detection Methods for CVE-2022-44670

Indicators of Compromise

• Unexpected crashes or restarts of the sstpsvc.dll or related SSTP/RRAS services
• Anomalous network traffic patterns on TCP port 443 associated with SSTP connections
• Unusual process spawning from SSTP service processes with SYSTEM privileges
• Memory corruption artifacts or access violation events in Windows Event logs related to SSTP operations

Detection Strategies

• Monitor Windows Event Logs for service crashes or exceptions involving SSTP components (sstpsvc.dll, rasman.dll)
• Deploy network intrusion detection rules to identify abnormal SSTP handshake patterns or malformed protocol messages
• Use endpoint detection and response (EDR) solutions to monitor for suspicious child processes spawned by SSTP-related services
• Implement Windows Defender Application Control (WDAC) to detect unauthorized code execution in protected processes

Monitoring Recommendations

• Enable verbose logging for Remote Access Services and VPN connections on affected systems
• Configure Security Information and Event Management (SIEM) rules to alert on repeated SSTP connection failures that may indicate exploitation attempts
• Monitor for unusual outbound connections from systems typically receiving inbound VPN connections
• Deploy SentinelOne Singularity platform for behavioral detection of post-exploitation activities following SSTP service compromise

How to Mitigate CVE-2022-44670

Immediate Actions Required

• Apply the Microsoft security update from the December 2022 Patch Tuesday release immediately to all affected systems
• Prioritize patching systems running Remote Access Server (RRAS) with SSTP VPN services
• If patching is not immediately possible, consider temporarily disabling SSTP VPN services and using alternative VPN protocols
• Review network segmentation to limit exposure of SSTP services to only necessary network segments
• Implement network-level access controls to restrict SSTP access to trusted IP ranges

Patch Information

Microsoft has released security updates to address this vulnerability as part of the December 2022 security updates. Administrators should refer to the Microsoft Security Update Guide for CVE-2022-44670 for detailed patch information and download links specific to their Windows version. The patches should be applied using standard Windows Update mechanisms, WSUS, or manual deployment procedures according to organizational policies.

Workarounds

• Disable SSTP VPN services if not required and migrate to alternative VPN solutions such as IKEv2 or WireGuard
• Implement network-level firewall rules to restrict SSTP (TCP 443) access to known and trusted client IP addresses only
• Deploy a Web Application Firewall (WAF) or network intrusion prevention system (IPS) in front of SSTP endpoints to filter potentially malicious traffic
• Consider using Azure VPN Gateway or other cloud-based VPN solutions that may receive patches more rapidly

# Disable SSTP on Remote Access Server (if SSTP is not required)
# Run in elevated PowerShell on RRAS servers
Set-VpnServerConfiguration -SstpPorts 0
Restart-Service RemoteAccess

# Alternatively, disable the Secure Socket Tunneling Protocol Service
Stop-Service SstpSvc
Set-Service SstpSvc -StartupType Disabled

# Verify SSTP is disabled
Get-VpnServerConfiguration | Select-Object SstpPorts